7B.5 IDENTIFYING CRITICAL STRENGTHS AND LIMITATIONS OF CURRENT SYSTEMS

Jennifer F. Newman 1, Daphne S. LaDue 2, and Pamela L. Heinselman 3

2Center for Analysis and Prediction of Storms University of Oklahoma, Norman, Oklahoma

3Cooperative Institute for Mesoscale Meteorological Studies University of Oklahoma, Norman, Oklahoma

.1. INTRODUCTION et al. 2007), advances in radar technology since the early 1980s, and the lead time involved in the The year 2008 marks the 20 th anniversary research, development, acquisition, and of the final design for the Weather Surveillance deployment of new systems have motivated the Radar1988 Doppler (WSR88D), a mechanically consideration of a replacement system or family of rotating Sband radar. This design milestone was systems (National Academies 2002; National preceded by a ~30year effort focused on the Academies 2008). research and development of Doppler weather A technology currently under (Whiton et al. 1998). Prior to its initial consideration is phased array radar (PAR). PAR acceptance as a replacement radar technology in technology, employed for decades by the 1979, was the achievement of nearly 20 years of Department of Defense to track aircraft and other Doppler research (1960–1979) and airborne targets, is now being examined to assess the execution of the Joint Doppler Operational not only its weather surveillance capabilities (Zrnić Project (JDOP: 1976–1978). Through the 1980s, et al. 2007; Heinselman et al. 2008), but also its the leadership of the Joint System Project Office capability to provide simultaneous weather and and continued radar research by scientists of the aircraft surveillance, termed multifunction phased Interim Operational Test Facility at the National array radar (MPAR; Weber et al. 2007). The Severe Storms Laboratory (NSSL) brought forth unique features of PAR technology are the the final design and funding for the WSR88D capabilities to rapidly and adaptively sample network. By 1997 these and other efforts storms volumetrically from an Sband antenna in culminated in a network of 158 WSR88Ds that scales of seconds instead of several minutes serve as the primary system used for operational (Zrnić et al. 2007). surveillance of radardetectable weather by the The first comprehensive look at employing National Oceanic and Atmospheric MPAR technology was provided by the Joint Administrations’ (NOAA Action Group for Phased Array Radar Project NWS; hereafter NWS). (JAG/PARP; OFCM 2006). An important Continuous improvements to the WSR component of the JAG/PARP report is a 88D system hardware and products (Crum et al. compilation of the current and future federal 1998; Serafin and Wilson 2000) have resulted in agency needs that radars can meet. The JAG significant service improvements, including attained this information through each agency’s increased mean warning lead time for tornadoes response, e.g., NOAA/NWS Office of Science and from 6 to 13 minutes, and reduced related Technology, to a survey. This survey was injuries (40%) and fatalities (45%; Simmons and designed with openended questions to attain Sutter 2005). However, the approach of this information about capabilities and requirements of system toward its 20year design life cycle (Zrnić current radar systems, and anticipated additional future needs (Appendix G, OFCM 2006). Though including federal agency needs in 1 Corresponding author address: Jennifer F. the JAG/PARP report is a noteworthy first step Newman, Cornell Univ. Dept. of Earth and toward the research and development of a Atmospheric Sciences, Ithaca, NY 14853; email: replacement radar technology, this research [email protected] (Newman). Readers may also process would strongly benefit by involving a contact LaDue: [email protected] or Heinselman: broader spectrum of users of weather radar [email protected]. information. As discussed by Morss et al. (2005),

incorporating user needs at the beginning and 2. CRITICAL INCIDENT TECHNIQUE throughout the research and development process is pivotal to producing the most usable scientific The CIT is an effective way of gathering knowledge or information. This user inclusive, specific, factual information about human iterative process is termed “endtoendtoend” behavior. The CIT has been used to conduct research (Morss et al. 2005). To maintain the studies in a variety of fields and is a popular, important operational capabilities of the current easily adaptable method in qualitative research radar systems, such as the WSR88D, and (e.g., Oliver and Roos 2003; Kraaijenbrink 2007; address its operational deficiencies, the strengths Schluter et al. 2008). The CIT was used for this and limitations of the system and their effects on study to attain specific information about radar users must be assessed. capabilities and how these capabilities affect The purpose of this study is to explore the operations. strengths and limitations of current radar systems Flanagan (1954) defines an incident as identified by users within two stakeholder groups: “any observable human activity that is sufficiently NOAA NWS and broadcast meteorologists. NWS complete in itself to permit inferences and meteorologists were chosen because the mission predictions to be made about the person of the National Weather Service makes clear the performing the act.” A critical incident must have a central role of the NWS in providing weather clear purpose and consequences with definite forecasts and warnings, as well as most of the effects. In this study a “critical incident” is an event weather data then used by others (see "NWS that illustrates how the strengths and weaknesses Mission" footnote). Current radar systems, in of weather radar affect a meteorologist’s ability to particular the WSR88D, are important data perform his/her job. sources used in the production of NWS products. The practice of asking for critical incidents Broadcast meteorologists represent a second, can be traced to the studies of Sir Frances Galton critically important stakeholder group. Several during the 19 th century. However, the CIT as it is studies have confirmed that most people receive known today began to evolve during World War II. and monitor weather information from their local During that time, the United States Air Force TV broadcasters, be it during severe convective needed a way to select and train pilots as quickly weather (e.g., Legates and Biddle 1999, and as possible. To help them attain this goal, the Air Schmidlin and King 1997), flooding (e.g., Hayden Force enlisted the help of John C. Flanagan and et al. 2007), or winter weather (e.g., Drobot 2007). the newly formed Aviation Psychology Program In this study, PAR is not presupposed as (Flanagan 1954). Their initial study sought to the answer to current radar deficiencies. Instead, determine why 1,000 pilots had failed training the suitability of PAR to stakeholders’ needs is programs and how these programs could be better assessed according to users’ lived experiences designed to produce competent pilots. An with weather radars. This approach, called the examination of the pilots’ evaluations revealed critical incident technique, allows us to see and many general, stereotypical statements — “lack of understand users’ current radar needs and how inherent flying ability”, “poor judgment”, radar capabilities affect operations. “insufficient progress.” Flanagan asserted that it An explanation of the CIT is given in would be much more useful if the evaluations section 2. Section 3 describes the data collection contained incidents in which pilots showed these and analysis methodology. The results of the qualities. study are discussed in sections 4 and 5, including To attain this information, Flanagan the role perception of each stakeholder group and developed a questionnaire and distributed it to the radar strengths and limitations identified by flight instructors, asking them about pilots’ each group. The suitability of phased array radar behavior during critical situations, and why this (PAR) technology to stakeholders’ needs is behavior was either effective or ineffective. The assessed according to these critical radar information gained from this study helped to capabilities in section 6. develop a new training program for pilots (Flanagan 1954). Under the guidance of Flanagan, the CIT was developed further and given its present name. The CIT is now a common and wellrespected method in qualitative research.

Critical incident interviews tend to each Two key stakeholder groups were include anywhere from a few to several incidents, selected for interviews, NWS meteorologists and depending on the length of the interview and story broadcast meteorologists. NWS meteorologists telling propensity of the particular interviewee. If were chosen because the mission + of the National researchers desire to compile a comprehensive Weather Service makes clear the central role of list of needs, as many as 100 incidents may be the NWS in providing weather forecasts and necessary before no new needs arise in interviews warnings, as well as most of the weather data then (e.g., Dunn and Hamilton 1986). For the purposes used by others (see "NWS Mission" footnote). of this demonstration study, we needed to scale Broadcast meteorologists represent a second, and the work down to a level that could be completed critically important stakeholder group. Several within a sixmonth time period. Our goal was to studies have confirmed that most people receive identify at least three major operational and monitor weather information from their local deficiencies for each stakeholder group and thus TV broadcasters, be it during severe convective illustrate the value this type of approach brings to weather (e.g., Legates and Biddle 1999, and the early development stages for new Schmidlin and King 1997), flooding (e.g., Hayden technologies. et al. 2007), or winter weather (e.g., Drobot 2007). In the end, nine interviews were 3. DATA AND METHODOLOGY conducted with participants in the Southern Plains of the United States, including five NWS The data for the study were collected forecasters and four meteorologists from the through interviews with radar users from two key broadcast community. Of the five participants stakeholder groups. The rational for choosing working at NWS offices, four were in management certain participants is explained, along with how positions where they played a variety of roles interviews were conducted. Because our study during weather events, and one was a lead plan involved interaction with individuals to elicit forecaster who primarily worked the radar desk stories about their work experiences, all during severe weather. Of the four participants researchers completed online training in how to working as broadcast meteorologists, three properly conduct such research. Our study plan primarily worked as onair meteorologists, one was submitted and approved by The University of also did field reporting during weather events, and Oklahoma's Office of Human Research Participant one was primarily a weather producer. Protection, a.k.a. Institutional Review Board, before data collection began. 3.2 Interviews Data from interviews is rich and complex, requiring a systematic approach to reliably Interviews were conducted at times and identifying meaning. Our approach is described. locations convenient to the participants, and used This section then closes with a brief discussion of the CIT as described by Dunn and Hamilton potential issues of trustworthiness relevant to this (1986). Dunn and Hamilton stress the importance study. of establishing rapport within the first few minutes of an interview, believing it is counterproductive to 3.1 . Participants ask for critical incidents right away. We established rapport at the beginning of each A purposive sampling strategy (Patton interview by asking participants to describe their 1990) was used to strategically select participants for interviews. Participants were selected based + NWS Mission: "The National Weather Service on their roles during weather events and their radar experience. Our goal was to gather provides weather, hydrologic , and climate forecasts and warnings for the United States, its territories, information from people who have worked with a adjacent waters and ocean areas, for the protection of variety of radar systems, both before and after the life and property and the enhancement of the national establishment of the current WSR88D network, and with people who serve in a variety of roles economy. NWS data and products form a national during weather events. Participants were information database and infrastructure which can be responsible for providing warning information to a used by other governmental agencies, the private sector, the public, and the global community (NWS, variety of users, which, in turn, strongly affected 2008)." their use of radar.

roles and responsibilities during weather events. In larger context of the job for different kinds of the main part of the interview, participants were weather events, methods of mitigating radar asked to describe critical incidents in which radar deficiencies, and experiences with other radar affected their ability to perform their job, and the systems. degree to which this was dependent on the type of weather event or the time of day. Finally, the 3.4 . Interrater Reliability participants were asked to describe the information they can obtain from current radar Codes that are consistent have achieved systems and how this differs from other radar interrater reliability (Boyatzis 1998). Two of the systems they have used. Participants were also researchers (Newman and LaDue) independently asked to describe their ideal radar system. coded interview transcripts and grouped codes into themes. A thorough comparison was then 3.3 Coding and Thematic Analysis done on one interview selected at random. Only minor changes were made to what turned out to Interviews were first transcribed verbatim be extremely consistent coding schemes. A in order to put the data in a form conducive to consensus on codes was easily attained. The analysis. Transcriptions constitute raw, complex, interrater reliability process helped to assure that and undigested data. In order to discover and the coding was likely repeatable and reliable, and make sense of that data, transcripts were that it was unlikely that any important issues were summarized using a technique known as coding. overlooked. Coding is a systematic way to organize interview data by applying labels that either summarize 3.5 Addressing Trustworthiness themes found in portions of text or are in vivo codes, literally the words of the interview (Gibbs Addressing biases or sources of error is 2002). By coding interview transcripts, researchers important for any kind of study and is commonly can more easily identify themes emerging in the addressed outright in qualitative research to help data, reorganize data according to similar ideas, readers judge the extent to which they can trust and compare ideas across interviews (Patton the data and results. Such admission and 2002). discussion demonstrates that the researcher is Research design drives both the approach aware of his/her prior beliefs or expectations and to coding as well as the subsequent analysis. is working to handle these as effectively as Because this study was an openended possible. Personal biases are more obviously in exploration of what two key stakeholder groups play in qualitative research than in the quantitative perceived as critical strengths and limitations of approaches more common in meteorology, but are current radar systems, a datadriven, thematic present in both. Methodological researchers in the analysis was appropriate (Boyatzis 1998). In a social sciences have therefore proactively datadriven approach, themes emerge naturally incorporated address of personal biases into from the data rather than being preconceived. research design and analysis strategies in a more After initially allowing the data to drive code thorough way than how most quantitative formation, the researcher might then use theory or approaches are undertaken in meteorology. prior research to guide articulation of the themes. The interrater reliability stage is an In our case, the maturation of our codes arose important step in establishing trustworthiness from our questions about how critical strengths because two researchers compare independent and weaknesses of current weather radars analyses, thereby revealing at least some affected participants' abilities to fulfill their roles. personal insights and biases in the interpretation Over eighty categories and subcategories and summary of verbatim transcript information were grouped into themes found across the (Patton 2002; addressed in the previous section). interviews. Several themes related to aspects of For the critical incident technique specifically, how radar strengths and limitations affected the researchers have stressed the importance of participants' abilities to fulfill their role, with role addressing biases at each step of the critical emerging as an unexpectedly important theme. incident research process — sampling strategy, The participants' roles provided critical context for data collection, and interpretation (e.g., Flanagan how radar was used by each stakeholder group. 1954). Additional themes included how radar fit into the

Significant bias could obviously arise from actually did, but the question had a second who participates in the study (sampling strategy) purpose as well. Questions about role would put because this kind of study reflects the participants' interviewees at ease, help them get into a frame of concerns and points of view. Readers are mind where they become the teacher to the informed about the sampling strategy for interviewer, and help the interviewer and participants and are discouraged from broadly interviewee to establish some rapport. In most extending results to all NWS meteorologists and cases, the interviewee and interviewer (LaDue) did TV broadcasters. not know each other prior to the interview. Another bias could arise from when and During analysis it became clear that where data were collected: all nine interviews participants' views of their role were a fundamental were conducted during the late spring and early context for understanding how successes and summer in the Southern Plains region. Severe issues with current radar technology manifested in convective weather would naturally be at the each participant's work. Explanations of the roles forefront of everyone’s minds. Severe weather interviewees articulated are presented first so the events dominated most of the interviews. To help reader may also gain this insight before delving address this bias, we probed for stories involving a into the weatherspecific successes and issues variety of other types of significant weather during interviewees related in their interviews. the interviews. The last potential bias for a CIT study— 4.1 National Weather Service Forecasters interpretation—could involve not only the researchers' personal interests but also National Weather Service forecasters said professional ties. Professional biases add a layer their main role is to make the best forecasts and of complexity: This study was funded through the warnings possible using the latest scientific NOAA National Severe Storms Laboratory's understanding of weather. During weather Multifunction Phased Array Radar project. Funding situations where radar is a primary tool, one or could conceivably influence the researchers' more forecasters may be dedicated to radar pursuit of information during interviews and choice interpretation and issuing warnings. During other of information to highlight in reporting. Three types of events, including winter weather, routine actions were taken to mitigate these potential roles such as the shortterm forecast desk may sources of bias. First, the project was sub become the office's most critical responsibility. contracted to The University of Oklahoma to a While some forecasters are assessing the current Center for Analysis and Prediction of Storms and anticipated state of the atmosphere and researcher and a Research Experiences for issuing public products, others are coordinating Undergraduates student, neither of whom have and assuring that external communication been involved in design or development of channels are working to both provide forecasters replacement technologies for the WSR88D. with weather reports and to assist certain user Second, the critical incident technique is an open groups like city or county officials. Occasionally ended questioning technique that elicits forecasters have the opportunity to work in an information on the problems interviewees incident meteorologist role, such as working encounter while performing their jobs. Further, the directly and onsite at a wildfire command post. interview format, by nature, brings out whatever Forecasters characterized their role as issues are prominent on a person's mind (Patton one of driving the warning notification process. 2002). Third, participants were given an early draft Their products are publicly available, and go of results and asked whether the results fairly directly to the public through a few channels like represented their points of view. NOAA Weather Radio and some public radio stations. But in many cases NWS information is 4. PARTICIPANTS’ PERSPECTIVES ON THEIR repackaged by another entity like broadcast ROLE meteorologists. While some forecasters are applying current scientific understanding and tools The interview guide designed for this available to assess the weather to issue study began with a question asking each person to appropriate forecasts and warnings in a timely explain his or her role during weather events. manner, other forecasters in each NWS office are Answers would assure we were not making receiving and monitoring subsequent incorrect assumptions about what each person communications originating from emergency

managers, TV broadcasters, city/county siren participating in a chat room with his local NWS systems, etc. The NWS forecasters do what they office. This broadcaster stated that he greatly can to monitor all communications and help drive benefited from insights provided by the NWS and a consistent warning message. used the opportunity to provide information from his spotters and viewers back to the NWS. 4.2 Broadcast Meteorologists In closing, the following summary of what interviewees shared about their lived experiences Broadcast meteorologists stated their with current radar technology relates strongly to main role is to deliver timely, accurate information how they view their roles. NWS forecasters are to the public and inform them of the safety focused more on the pure scientific aspects of precautions they need to take. All the broadcast weather detection, with attention also given to meteorologists we spoke with worked at television communication. Broadcasters are focused more stations with highresolution radars that had fast on conveying a threat to viewers, with attention update times of 30 s to one min, which they found also given to a scientific assessment of what is extremely useful to do their jobs. By examining happening. NWS forecasters need to assess the their high spatial and temporal resolution data at current and likely threats to make warning the lowest elevation angle, broadcast decisions. Broadcasters need to assess current meteorologists are often able to interpret and and likely threats to figure out what their message narrow down the threat area within warnings should be, how urgent it needs to be, and what issued by the NWS. form that message might take. NWS forecasters As part of their role, broadcast focused on radar as a primary decisionmaking meteorologists often show radar images on the air tool. Broadcasters used radar in that way, but to illustrate the current weather threat to viewers. focused their stories on how radar could be used However, since the general public is not familiar to convey a threat to a nonscientist. These with radar data, they told us that sometimes onair complimentary roles are each critically important interpretation was required to help viewers to what has been called the integrated warning understand what they were seeing. The "big red system (Doswell et al. 1999), which is in actuality blobs" were obviously important, but viewers did an ad hoc system of disparate parts that usually not necessarily appreciate the importance of a desire to function in harmony, each adding value. hook echo. Our broadcaster participants all had The integrated warning system does not have an meteorology degrees (common in the Southern overall structure guiding that interaction and those Plains) and so struggled somewhat with being complementary roles. The functioning of the so both a meteorologist and a communicator of called system depends entirely on the people weather information. They said it is difficult to within it. Our participants were cognizant of interpret radar data while the cameras were rolling playing roles within that ad hoc system and — while mentally doing a sophisticated radar explained their successes and issues with current analysis, they need to be giving simple, radar systems within that context. understandable information to their viewers. For the purposes of brevity, "broadcaster" Although broadcast meteorologists receive is used to refer to our TV broadcaster participants, uptotheminute warnings and other official "forecaster" to our NWS forecaster participants. products issued by the NWS, they wanted to know Meteorologist is used to refer to both groups at the reasoning behind these warnings and when once. the NWS is considering issuing a new warning. All the broadcast meteorologists noted that 5. SUCCESSES AND ISSUES WITH CURRENT anticipating warnings issued by the NWS would RADAR SYSTEMS help them make wiser decisions about when to cut in with severe weather coverage and what The primary current radar system NWS information to show or discuss on the air. For forecasters used for weather detection was the example, one broadcast meteorologist mentioned network of WSR88Ds. That network was noted his frustration that on a few occasions, after for its dependability and availability — unlike many interrupting regular programming to provide other data sets, such as upperair, surface, and severe weather coverage, he went offair only to rain gage data, radar is available throughout the discover that the NWS had just issued a warning. NWS areas of responsibility and is frequently Another broadcaster, however, had the privilege of updated. Said one forecaster, “...it’s there twenty

four hours a day and it’s pretty reliable, and we’ve beam widths, approximately 150m range bins learned to trust the data.” Stories focused on radar (dependent on choice of PRF), and 30s to 1min as a primary tool for many types of weather, such updates. This high temporal and spatial resolution as severe weather, but participants touched into data was available immediately, providing distinct its utility in a wide variety of situations. advantages over WSR88D data. More than one Some NWS participants had recently described how, in a fast scan mode, the station gained access to Terminal Doppler Weather radar data made storms looked alive. Station Radar (TDWR). They said TDWR had higher radars were poorer quality, however, and spatial and temporal resolution than WSR88D, broadcasters cited many issues that affect their but only specified the time aspect: updates on the radars. Those radars are subject to the same order of 1 minute. Stories only conveyed where types of ground clutter issues as the WSR88D, TDWR added information, neglecting any but then also have a tendency to smear in fast limitations or problems with that data. Certain scan modes, have significant 2 nd trip echo types of incidents highlighted the value that high problems, significant attenuation, and range and spatial and temporal data is beginning to bring to velocity folding—the latter beginning as low as 33 NWS operations. Those forecaster stories mph. None of the broadcaster participants said involving TDWR data were very similar to the they were running any local algorithms because of types of features and information that the processing requirements and the length of broadcasters gain from their station radars. time needed. Broadcasters participating in this study all Following are the types of problems or had both a station radar and access to data from situations that arose in forecaster and broadcaster the WSR88D network. WSR88D data was cited participants' stories. These problems and as having betterquality velocity and reflectivity situations may not encompass the possible range data, detecting echoes at longer ranges and of ways radar is used in weather contexts; they without the major second trip echo problems of represent what arose during the nine 1hour television station radars, and always including interviews. In most cases, stories helped situate volumetric scans. At times, WSR88D reflectivity radar in the context of the work challenge, allowing data were used by itself in a corner or inset the value and limitations of current radar systems graphic to convey threats without breaking into to become clear. The leading section is an regular programming. One older broadcaster example of how more general comments rounded emphatically stated that the WSR88D, and the out the content of specific stories. All information subsequent improvement in warnings from the in this section arose during interviews. NWS, had made his role much easier to fill. Broadcasters use WSR88D information to 5.1 Identifying Storm Type, Strength, and supplement their own radar data, but update time Current and Likely Threats was a major concern of all broadcast participants. One participant explained that because of financial NWS forecasters all emphasized, usually limitations, his station had to wait up to eight at the outset of the interview, that they work to minutes to obtain volumetric scans from the make the best of the science with radar as a nearest WSR88D radar. The time delay had a primary tool during severe weather situations. significant impact on them, with the data being Forecasters explained, for example, that science essentially "useless" when storms were moving provides 3D conceptual models of severe storm quickly. One pointed out that old data does not processes that radar then either directly or help in offair analyses and cannot be used onair indirectly indicates, including: bounded weak echo to convey a current threat. One broadcaster regions, elevated high reflectivity cores, strength characterized the WSR88D as a "shotgun of storm updrafts, 3body scatter spikes, method" to get an overall picture of everything, but , storm top divergence, rear inflow with far less detail and sometimes significant time jets to storm complexes, location and movement delay. of boundaries, surging rear flank downdrafts, All broadcasters spent a significant portion tornadoes embedded in areas, of the interviews talking about how their station likelihood of widespread wind damage, and storm radars played a critical part in how they fulfilled type. Radar indications of these 3D storm features their role. When details were given, the station are critical indicators of storm type, strength, and radars were described as 5cm radars with 0.08° current and likely threats. In other words, the radar

indications of these features are essential to NWS move through a radar domain. This results in at forecasters in making good warning decisions. least two challenges for forecasters. One of the Along this general theme, forecaster older forecasters said younger forecasters have to participants told some stories of how other tools learn how the same storm features will change in interplayed with radar during specific events. A appearance as the storm is sampled at different few stories involved wanting to remain aware of heights. Another forecaster remarked on the the larger environment and how that might be constantly changing magnitude of the distance changing through their forecast area over time. between the sampled storm feature and the One forecaster gave an example of using a fine ground. The higher the feature, the less certain scale numerical weather prediction model to see they are of where—and whether—that feature is variations in wind shears within his forecast area. impacting the ground. Broadcasters also On more than one occasion the fine scale model mentioned that it was a challenge for them and helped his office anticipate changes in storm type their competitors to remain cognizant of height and the onset of damaging weather from changes aboveground as they attempted to relate radar in the environment, the latter being something a information to likely impacts on the ground for their radar cannot usually detect. Forecasters also viewers. reported an increasing reliance on environmental clues at longer distances from the radar. 5.2 Anticipating and Detecting Tornadoes Characterizing this sentiment, one forecaster commented that it is easy to concentrate on radar Not surprisingly, tornado situations information, so he has to remember to "back out" dominated stories from our early summer and look at other data to do the best science. By interviews with participants from the Southern using environmental clues and model data, Plains. Participants from both sectors wanted to forecasters said they could anticipate and watch anticipate tornado touchdowns, accurately choose for radar indications, rather than only react once not to warn as much as to accurately warn, and those indications were prominent. frequently update information for their users. When the subject of volumetric information Participants, particularly the broadcaster arose in interviews with broadcasters, it was in participants, told many stories related to context of monitoring storm trends to help them nonroutine situations where they could see decide when and how to cover early phases of complex tornado processes in unprecedented storm events. They mentioned using trend detail. Otherwise, participants had a tendency to information in part to try to anticipate warnings gloss over the wellestablished, nowroutine uses from the NWS and to generally keep viewers of WSR88D, emphasizing instead those apprised of changes in storm strength, particularly situations where they had to infer beyond what increases in strength. One broadcaster mentioned current radar could directly detect and use using volumetric information specifically in the additional information to best fulfill their roles. context of downbursts (see later section on Now that forecasters have the incredibly Damaging Winds). But as subsequent sections will valuable velocity information that Doppler radar reveal, broadcasters' selfidentified role of adding provides, they have become more aware of how meaning and narrowing down the threat area quickly storms can evolve. In particular, they have within warning messages from the NWS meant observed many cases where the transition from a their stories emphasized use of lowlevel, rapid nontornadic to tornadic mode took place between scan information. In addition, one broadcast WSR88D volume scans. Three forecasters had meteorologist we spoke with explained that the seen people in their office restart a volumetric processing time for a volumetric scan with his scan in order to get a faster update at the lowest radar was so long that his station’s radar was elevation angle. Doing so took valuable time away often left on the lowest elevation angle. Again, he from radar interpretation, but forecasters were was more interested in controlling the radar strongly motivated to have more frequent scans himself, doing sector scans on storms of interest. when marginal or rapidly evolving storms were Current radar system configuration over urban areas so they could make the most provides a challenge. Forecasters said they must accurate warning decisions. learn to remain cognizant of the constantly All NWS forecasters said it was as changing height above ground of where radar is important to correctly choose not to warn as it was sampling within individual storms as those storms to warn, but current radar systems only sometimes

provided adequate information to enable warnings far from the radar must encompass a forecasters' confidence. One particular instance larger area due to the inherent uncertainty in occurred after many people had gone to bed. The ground location. storm was close enough to the WSR88D that the One broadcast participant similarly noted forecaster could see that the had that WSR88D network coverage was a limitation been undercut, preventing tornado formation. The at a television station where he had previously forecaster was happy to have sufficient radar worked. That station did not operate its own radar, information to make a correct decision not to warn: so broadcast meteorologists there relied He was aware of more than one instance where completely on the WSR88D network. After having someone lost their life while taking tornado worked at a television station with its own radar, precautions. Warnings also, he said, cause this participant realized the vital information he businesses to close and disruption to those who had been missing. drive to alternate locations for shelter. Storm Forecaster participants who had access to spotter information is typically helpful in making up TDWR data discussed the advantage of having for inadequate radar data, but one forecaster rapid, lowlevel updates. One forecaster mentioned that many of their storms occur after mentioned that greater spatial and temporal dark, emphasizing the principal role of radar resolution at lowelevation angles helped him information during warning events. understand the evolution of shortlived features — Radar was also the primary information “tornado cyclones, tornadic vortex signatures, going into warning situations for many marginally microbursts, circulations that form on gust fronts.” severe events. In some of those marginal events, He described a late spring event in which a violent particularly those outside spring, spotters are not tornado first touched down in a metropolitan area. as alert or numerous. One story illustrated how TDWR was wellpositioned to observe the storm, current systems may not be ideal. In this story, a allowing this forecaster to see a rapidly developing landspout tornado was correctly inferred because mesocyclone with intense convergence. This a boundary was likely intersecting with a storm. information gave the forecaster confidence to But the storm was just far enough away from the intensify his warning message, because he knew radar that the actual intersection and subsequent tornadic development was imminent. TDWR was lowlevel circulation was not sampled. The tornado also cited as helping narrow down the area that occurred was brief but did some minor encompassed within a warning. One forecaster damage. related an instance where he was fairly confident Some tornadoes occur with rotation of a tornado location to within about onequarter initially only at low levels. In some of those cases, mile. the midlevel mesocyclone that current systems Broadcasters spent most of their could detect develops only after the tornado is interviews talking about their own radars, already causing damage. In one forecaster story, particularly in the context of tornado situations. a tornado was on the ground for over 6 miles Their radars all had fast, lowlevel scanning before a classic radar signature was sampled. capability and were situated in the metro areas When midlevel signatures did show where their viewers were most heavily tornadic potential, but storms were far from the concentrated. Television station radars at all radar, forecasters reported their warnings were broadcast participants' stations enabled them to issued with a different mindset that accounted for detect smallscale signatures that occurred on detection limitations. Because forecasters have time scales of one minute or less. One participant less understanding of what is truly happening near spoke about the detailed storm structures she had ground level, they tend to issue warnings earlier. never seen before. She stressed the importance of One participant added that he is more likely to being able to react to these rapid changes, issue a warning for a storm at a long distance because many recent signatures were significant because he often does not have sufficient quality and produced damage. information to help him decide when not to warn. Particularly once weather is occurring, Storms are generally tilted or sheared from the broadcasters want to add detail to warnings in vertical, meaning the radardetected circulation order to help viewers understand and properly may be several miles from the ground contact. react to the threats. They described instances The result of the likelihood of storms being tilted where they had confidence to specify exactly from the vertical, one forecaster reported, is that where the most dangerous part of the storm was

located and relate that threat to where people downdrafts. One of the forecasters specifically lived. Broadcasters overlaid their station radar pointed out that the slow volume coverage reflectivity data with major road arteries and patterns preclude detecting a rapidly descending incorporate information from storm spotters and core in reflectivity data as the core was still falling. viewers. Often their confidence came during The descending cores typically took place on the situations where the small beam width and rapid order of the time it took to complete a volume updates of their television stations radars could scan. TDWR, which is relatively new to NWS pinpoint the threat. Just as NWS forecasters felt it operations, was available during one recent was important to accurately not warn, downburst situation. The forecaster who broadcasters want to help people know when they mentioned it said TDWR data helped him amplify will not be affected just as much as when they will. his warning message. Again, however, the radar For instance, one broadcast participant spoke was detecting a downburst inprogress. about a spring 2008 event in which two tornadoes touched down within an hour, producing minor 5.4 Identifying and Warning For damage in a metropolitan area. Warnings were issued in the middle of the night, and people woke Forecasters further explained that up, confused and scared, to emergency sirens. because radar is poor at detecting severe winds at After examining data from his highresolution ground level, hail is often the basis upon which radar, the broadcaster issued statements over the severe warnings are issued. Current radio that related the tornado locations to familiar systems do not directly detect hail size. streets, assuring people that if they lived west of a Forecasters cited using 3body scatter spikes and particular street, for example, they would be safe. the height and strength of reflectivities in certain He felt that pinpointing the affected area helped temperature ranges to help them infer the keep people calm during this particular event. presence of hail. Forecasters also mentioned Although station radars were clearly superior to using environmental information to help decide the WSR88D in pinpointing threats, one broadcaster likelihood of hail. Most algorithms were unhelpful, said he was aware of a few recent minor events though the recent Maximum Expected Hail Size that even station radars were not detecting. algorithm was citing as being better than past algorithms in indicating storms with hail. 5.3 Other Types of Damaging Wind Events One forecaster illustrated why hail detection can be critical: weather impacts can vary Participants from both sectors made it widely depending upon what and how much very clear that downbursts and heatbursts are precipitation is falling. Likewise, warning among the most difficult types of damaging messages ought to convey the threat accurately. weather to detect with current radar systems. Two In the case of hail, the same reflectivity signature forecasters and one broadcaster pointed out that accompanied by 60 – 70 mph winds could indicate the motion of the falling core in a downburst was smaller hail that "isn't life threatening" or baseball essentially tangential to the radar, so was not size hail for which "people ought to be taking visualized in velocity information. They went on to tornado precautions." One forecaster related a explain that inadequate sampling of low levels situation of an earlyseason, highprecipitation meant that divergence signatures may not be that appeared to have large hail. He was detected at all, but even where radar does sample still surprised his office never received reports of at ground level, a divergence signature means anything larger than quartersize hail during that damage is already occurring. One broadcaster event. cited a specific example of a recent, undetected Broadcasters were also wanting to detect downburst that occurred at 8 o'clock in the and convey hail threats to viewers. One morning over a place people were congregating. specifically noted that people can take mitigation Being able to anticipating a downburst actions, such as moving cars into garages, if they was important for our participants and they gave have adequate warning of large hail. Broadcasters examples of how they attempt to do so. Volumetric were all very skeptical of radarderived hail sizes. information provided the best clues to help One broadcaster, who often reports from the field, forecasters anticipate a downburst. Two said he has become more and more daring to forecasters mentioned looking for convergence at drive into storms to see what is there and has midlevels and monitoring surging rear flank

rarely ever found hail as large as radar 5.6 Monitoring Trends, Evolution, and estimations. Transitions

5.5 Rain Events Time and process are critical in monitoring trends, detecting transitions between weather Radar information assists forecasters in types, and seeing evolution of the boundary layer knowing the areal extent of rainfall and is and environment prior to the development of sometimes the first indicator of flooding situations. weather. Because radar information is available at Radar provides information everywhere and a 5min time interval, radar information provides approximately every 5 minutes. Gage data varies forecasters and broadcasters with a way to from manual reports to automated reporting; monitor many types of trends and transitions, and automated gages may have a slow reporting gain a sense of the processes taking place in the interval. Although rainfall estimates derived from atmosphere. radar data can be inaccurate, both forecasters and Forecasters mentioned that they used the broadcasters said radar at least provides a useful time element of radar to help them identify qualitative assessment of where the greatest transitions from one type of weather to another. amounts of rain may have fallen. Forecasters also For example, one forecaster noted that because use storm total, 3hour, and 1hour radar radar was always there and covered a large area, estimates of accumulation. One participant said he could use it to look at synopticscale changes. that he also uses radar during severe weather Similarly, one broadcaster mentioned using long events to identify the transition from a primarily loops to illustrate the overall movement and severe hail and wind phase into a flooding phase, development of weather systems to viewers. looping base reflectivity to determine where heavy Another forecaster mentioned using radar loops to rainfall is starting to occur. anticipate severe thunderstorm winds by watching Providing flash flood warnings is a major a precipitation core catch up to the leading edge of function of the National Weather Service, but thunderstorm outflow. Prior to convection, a participants said radarestimated precipitation can forecaster told of a situation where he was waiting be inaccurate, challenging their ability to perform for evidence of a deepening surface low. The first this role well. There are presently two ZR indication was when increasing surface winds relationships forecasters use to see the areas of caused the character of clear air echoes to heaviest rainfall. One forecaster said he wished change. All forecasters and broadcasters told the radar could automatically switch to whichever stories of using radar to watch the evolution of was the best one for the situation. Broadcasters mesocyclones and tornadoes. also had learned not to trust radarderived rainfall Broadcasters, and those forecasters who estimates. Participants from both groups had seen TDWR data, told stories of detecting emphasized using ground truth to verify amounts. phenomena that occurred on shorter time scales In the specific case of tropical situations, than what the WSR88D can detect. As mentioned forecasters pointed out that the radar network earlier, storms have rapidly evolved from non configuration hampered adequate sampling. severe to severe modes in between WSR88D Tropical regime precipitation is generally volume scans. Broadcasters told many stories of distributed within the lower levels of storms and so using the high temporal frequency of station may result in deceivingly light echoes. At far radars to watch incredible detail in tornado ranges, radar might be sampling above the formation, evolution, and location. One forecaster highest precipitation regions. Tropical rainfall can said TDWR was helping him see aspects of be intense and surprising in impacts. One evolution he knew was happening, but could not forecaster knew of a situation where motorists see with WSR88D data. were caught offguard when encountering high water on roads that did not normally flood. 5.7 Boundary Detection

Another strength of radar brought up by all forecaster participants is its ability to detect boundaries; convergence zones and fronts, outflow boundaries, and dry lines are some examples. Boundary identification, evolution, and

movement are all critical in anticipating initiation of often wrong. "Large, wet snowflakes versus sleet convection and anticipating likelihood of tornado or ice pellets or snow pellets... affects the development. Many stories illustrated various accumulation," one forecaster said. Both aspects of the importance of boundaries. During forecasters and broadcasters have found they the 2008 severe weather season, forecasters must supplement radar information with phone watched the evolution and movement of calls to obtain ground truth. Such supplementary boundaries to anticipate rapid initiation of severe information is difficult to attain at night, when most convection. In a different situation, radar people are sleeping. A nighttime start to a recent information helped forecasters decide not to issue snow event meant a forecaster had little a warning because it showed that a rear flank verification about the event until morning. downdraft had undercut a storm circulation. Boundary detection has also been used to predict 5.9 Detection and Monitoring of Nonweather important wind shifts in nonweather situations. Events One forecaster recalled a large wildfire that dozens of firefighters were struggling to Several NWS forecasters stressed the extinguish. An incoming boundary caused a versatility of radar and how it can be used for a significant wind shift, and the firefighters had to variety of different nonweather events. One change their positioning. If radar had not been forecaster mentioned the importance of detecting used to detect this boundary, many firefighters boundaries and their movement during hazardous would have been seriously injured or killed. material situations. Such information is critical to Finally, radar detected the presence of a boundary those officials managing the safety of people that likely extended under a storm, helping nearby. A few participants mentioned using radar forecasters correctly infer a landspout tornado that to detect smoke plumes from fires and assess how was not otherwise detected. Unfortunately, high the smoke was rising. In some of those because boundaries are a relatively lowaltitude cases, radar detected wildfires before local atmospheric phenomena, radar cannot detect officials were aware of them. One participant was them at distances far from the radar. able to see debris from a space shuttle reentry on a radar image. 5.8 Frozen Precipitation Events 5.10 Clean and Accurate Data In winter situations, forecasters and broadcasters both need to determine the onset, Although information about the movement type, and intensity of winter precipitation. They of hydrometeors has been one of the greatest also mentioned that although winter situations advantages of current radar systems, and has generally occur on a large scale, radar helps them revolutionized storm detection and warning, identify areas of heavier precipitation or velocity information from current radar systems precipitation transitions within the larger event. remains imperfect. Forecasters cited cases where Participants said they used radar in two additional a storm moved into an area of purple haze in ways. They looked for an absence of radar echo WSR88D data. One forecaster, currently in a around the radar to infer that snow was not management role, said he actively watches for this reaching the ground near the radar. In a different potential and proactively changes the PRF so his case, one forecaster said he was able to warning forecasters do not have interrupted or accurately lower forecasted precipitation amounts dirty data. when those absences of echo near radars did not Because broadcasters had access to fill in. relatively clean, highquality WSR88D data, they Radar has potential to be a much more could generally work around the dealiasing and useful tool during winter precipitation events. One secondtrip echo problems that appeared to be forecaster mentioned that in certain winter characteristic of both specifications (e.g., 5cm situations snow can grow as it falls, but that the wavelength) and user settings (e.g., PRF) of their WSR88D network does not sample low levels in station radars. For example, when showing a all areas. A light echo has sometimes been particular case of an earlyseason tornado, one deceiving in regard to how much snow was broadcaster showed how his radar had a actually falling. Precipitation type and intensity are significant amount of secondtrip echoes dirtying particularly important in winter situations but are the display. He zoomed in on the storm of interest,

which he then presented in the very clean, high flagged where the signature is not necessarily resolution image he showed onair during the indicative of a tornado. Viewers understand that event. His station radar clearly showed the defined big red blobs (storm cores) are dangerous, but tornado circulation that was not detectable on the they do not necessarily appreciate how a tornado nearby WSR88D, only 12 miles away, due to its signature might appear in radar data. One poorer spatial resolution. broadcaster mentioned that he has become No negative comments were made about reluctant to show algorithm output on the air the quality of TDWR data. Such absence of because the numerous icons caused confusion in comments does not mean problems did not exist. viewers. But not showing algorithm output had an unanticipated consequence: a viewer called in, 5.11 Radar Algorithm and Display Tools accusing him of not caring enough about her area enough to show the little circles. All the broadcast Study participants were also asked about meteorologists stressed the importance of gaining how algorithm output and display tools for radar ground truth information to assess the reliability of helped them do their job. These questions were algorithm output. part of the closure phase of the interviews; stories Regarding displays, a few forecasters— of critical incidents were not requested. and all broadcasters—mentioned using Gibson Regarding algorithms, participants in this Ridge (GR) software (see study generally considered algorithms to be a http://www.grlevelx.com/) to visualize radar data. strength of current radar systems, but they cited Broadcasters said their storm spotters were significant problems as well. Certain algorithms plotting their GPS position on radar data using the were used frequently: stormrelative velocity, GR software in order position themselves. various precipitation totals for keeping track of Forecasters were using 3D tools, though one rainfall, hail and rotation swaths to monitor specifically said he was not interested in "flying potential damage corridors, and reflectivity cores through" a thunderstorm. He did, however, above certain temperatures to assess likelihood of appreciate being able to display radar data akin to hail. Other algorithms were primarily used as a the way a storm chaser might visualize the storm safety net, particularly when several storms were from the field. Other participants said they created occurring simultaneously. As mentioned cross sections of radar reflectivity using the GR previously, ZR calculations can lead to inaccurate software. precipitation estimates, particularly during tropical Forecasters valued conventional display rain events. Two broadcasters specifically noted tools as well. One in particular specifically that they are hesitant to show the storm total mentioned using a 4panel display to monitor precipitation image on the air, because they know storm top divergence and lowlevel signatures it is often an over or underestimate of the actual simultaneously. Another mentioned how incredibly rainfall. useful it was to directly overlay velocity and Two forecasters discussed the Maximum reflectivity to better understand how features Expected Size of Hail (MESH) algorithm, which related between the two types of radar uses a composite of radar data to calculate hail information. size. These participants found MESH to be much Ultimately one forecaster said he created more reliable than traditional hail size algorithms, certain displays that "get to the point," showing stating that it is a “quick way to confirm that this critical information he had learned to trust, that [storm] is severe or probably it’s not.” related to what was "impacting people on the All the broadcast meteorologists ground." Another said he valued things like the discussed how algorithm information both assists "Springfield curve," that were scientifically based and complicates their role. They have generally ways to color data to highlight features of become skeptical of algorithm information, though significance. Displays needed only to help them they need and value the potential that algorithms distill the important features from data; he did not can bring to their role. Algorithm icons can assist want to be distracted with long procedures to set them in conveying where tornado threats are most them up. likely, but most situations have many areas

WHAT IS TO ADDRESS WHY NEEDED WHAT PROBLEM Radar is often first and/or only source of data to indicate what is happening. Rain gages are far apart Meteorologists need to know what and reporting intervals vary. Other data is sparse is happening 24/7/365 (e.g., surface) or simply less useful in a definitive sense (e.g., satellite).

Forecasters need to focus Having to change the PRF to remove purple haze or Reliable, clean, attention on and problem-solving change the Z-R relationship to improve accuracy of accurate data skills on science rainfall takes valuable time away from operations. without intervention Broadcasters need to use WSR- 88D data to illustrate threats to WSR-88D data has been reliably clean, whereas viewers, sometimes as an inset station radars have data quality issues. graphic

Radar provides more frequent data and better areal Meteorologists need to know coverage than any other source of rainfall how much rain has fallen information, but precipitation estimates are very poor.

Figure 1: The set of issues in this figure (middle column) are related to one or more radar characteristic or capability that would mitigate that problem (first column). Issues are explained in the last box in each row. This figure shows the issues participants raised that are associated with not having reliable, clean, accurate data or having to manually intervene to assure data is that way.

6. DISCUSSION others (conceptual models and wildfire smoke detection) are linked to two capabilities. In a big The unique strength of study design like picture sense, meteorologists said they needed this one is that it begins not by asking for a mere the reliable, clean, and accurate data that WSR summary of what people think, but by asking them 88D currently provides. There were just a few data to share incidents that demonstrate how quality exceptions that required their intervention successes and issues with weather radars to mitigate or at least lessen (Fig. 1). Rainfall affected their ability to fulfill their roles. This study estimation was included here because of issues does not leave the reader wondering what was with accuracy. Precipitation characteristics are meant by what a participant said or why they more fully addressed as separate need discussed believed a certain item or capability was important. later in this section. The first section below summarizes the needs Figure 2 shows two related needs: high participants had in a new system and relates those temporal and highspatial resolution data. These needs to the issues they raised. needs were somewhat separable when Now that analysis of interviews is considering the issues those characteristics would complete, the authors reflect on how participants' address. One probable exception was data that needs relate to one of the replacement would allow meteorologists to recognize technologies currently under consideration, the conceptual models of storms. Depending on the multifunction phased array radar, or MPAR. conceptual model, both capabilities might be necessary. 6.1 Needs in a New System The characteristic most prominent in participants' stories was the need for consistent Nearly all issues could be easily data and lowaltitude data throughout the forecast summarized into diagrams showing the or coverage area (Fig. 3). Many important, radar capabilities or characteristics of weather radar that detectable weather features occur at low altitudes are needed, what problems that capability or either before or in the absence of midaltitude characteristic would address, and why participants signatures. Some weather processes only occur at said it was important. A few issues appeared relatively low altitudes: precipitation processes in related to more than one radar capability. One tropical regimes and snow growth. such issue (precipitation) is listed twice and two

WHAT IS TO ADDRESS WHY NEEDED WHAT PROBLEM

Tornado cyclone / mesocyclone The transition from a nontornadic to tornadic state evolution can occur on the order often happens between WSR-88D volume scans. of 30-sec to 1-min

Forecasters want to make the best warning decisions Need to detect evolution and High-temporal with adequate lead time for people to take transitions between storm resolution data appropriate actions. Broadcasters need to decide type when and how to cover the weather.

Need to detect a The motion in a downburst or heatburst is tangential downburst/heatburst before to the radar. A divergence couplet at the ground one is happening means the event is already in progress. Mid- and upper-level signatures are not reliably detected.

Understanding current and likely threats is critical to making the best forecasts and Need data that matches features of warnings and helping people make the best conceptual models of storm processes decisions.

Need to detect nonweather hazards, e.g., Forecasters provide support to other officials smoke from wildfires managing local situations.

Need ability to detect changes in the Anticipating convection helps forecasters stay environment prior to storm formation ahead of the weather.

High-spatial Warnings encompass a far greater area People are disrupting their lives to take action when resolution data than any possible tornado damage path they won't be affected by the weather; some have died taking such actions.

Meteorologists can misunderstand the true nature Some mesocyclones appear weaker than of a threat and subsequently not warn or not they really are far from the radar include verbiage appropriate to the threat. Figure 2: Like Figure 1, except these are issues associated with low temporal or spatial data.

The last several issues, shown in Fig. 4, radar characteristics, such as wavelength, concerned precipitation type, size, distribution of beamwidth, or network density. sizes, and intensity. Meteorologists appreciated The need for reliable, clean, and accurate the areal coverage of radar and the qualitative data (Fig. 1) is one that the Radar Operations sense of how rainfall or other precipitation was Center has adeptly attended to since the distributed across the area, but had learned not to deployment of the WSR88D in the 1990s. This trust radarderived precipitation totals. need also drove the design decision to deploy S In closing, WSR88D has revolutionized band rather than Cband radars, because Sband warnings to the point that forecasters and radars are impacted less by undesirable issues broadcasters alike are looking beyond to what such as attenuation, for example (Whiton et al. they believe is possible. Some stories related the 1998). As mentioned by interviewees, some inadequacies of WSR88D while most stories methods for producing the data quality needed to focused on how TDWR or station radars added a best do their job required their intervention. great deal of value to the warning and Examples mentioned necessitated adjustments to dissemination process. the PRF or ZR relationships, or even restarting a volume scan in midcycle to attain highertemporal 6.2 Suitability of PAR to Stakeholders’ Needs resolution data at low elevations. A potential solution to these important issues would be Some aspects of the four major radar situationdriven adaptive scanning, an needs found in this study (Figs. 1–4) are attainable advantageous capability of PAR. Additionally, PAR by the implementation of PAR technology, while can provide rapid scanning of low elevations others are only attainable by changing current without human intervention. Another component to this proposed solution is the implementation of

WHAT IS TO ADDRESS WHY NEEDED WHAT PROBLEM

Need information It is as important to accurately not underneath mesocyclones warn as much as it is to accurately to assess likelihood of warn. tornado formation Tornadoes sometimes occur without a Need information at low levels to mesocyclone present. see boundary-storm intersections Consistent and low- Tornado circulations do not always begin at mid- altitude information Need to detect low-altitude throughout area levels. Damaging tornadoes can be on the ground tornado cyclones that form for several miles before a mid-level mesocyclone Both groups struggle to without prior mid-level is apparent on radar. remain cognizant of changes mesocyclones in height-above-ground of Far from radar, warnings encompass more area due radar-storm intersection. Need to better infer tornado- to uncertainty in the possible tornado-ground Features change in ground intersection to narrow intersection. Broadcasters routinely add appearance because the down area encompassed information from station radars and storm spotters detected height in storm is within warnings to do what they can to pinpoint tornado threats for changing and likelihood of viewers. impact on ground. Tropical rainfall is distributed Accurate precipitation estimates are especially in the lower altitudes of important in tropical situations, where rainfall is storms often far above average.

Snow can grow as it falls, Snow can grow as it falls, meaning a light echo meaning a light echo far from far from the radar can be deceiving. radar can be deceiving

Figure 3: Like Figure 1, except these are issues associated with constantly changing heightabove ground of radar measurements and with the related issue of lack of lowaltitude information throughout the radar domain. dualpolarization, which promises to improve spatial resolution data that meteorologists have precipitation estimates and employ smart found useful (Fig. 2). applications of ZR relations where and when Other radar design options could also needed (e.g., Giangrande and Ryzhkov 2008). attain higher resolution data than the current The need for hightemporal resolution WSR88D system. Higher spatial sampling may be data to better identify and monitor fast evolving attained by designing Sband radars with smaller precursors to hazardous weather can be resolved beamwidths, or designing new radars with smaller by the fast scanning capability of PAR (Fig. 2; wavelengths that would be part of a more dense Zrnić et al. 2007; Heinselman et al. 2008). An radar network (e.g., McLaughlin et al. 2005). operational, fourfaced PAR would volumetrically These radar design options also offer a way to sample a storm at least four times faster than the provide the consistent and lowaltitude information WSR88D. Heinselman et al. (2008) showed the needed by meteorologists. improved depiction of storm processes resulting The need for more accurate information from volumetric scanning on the order of 1min for about precipitation type, size, distribution, and three storm types: a microburst, reintensifying intensity is one that will be addressed in the near supercell, and hail storm. future by the addition of dualpolarization In the short term, another option for capability to the WSR88D network (e.g., Ryzhkov attaining hightemporal resolution data is to et al. 2005; Scharfenberg et al. 2005). The dual continue the current trend of making TDWR data, polarization upgrade will include algorithms that which samples the 0.5 ° elevation angle every min, discriminate meteorological from accessible to the NWS (Istok et al. 2005). nonmeteorological echoes and classifies a suite of Because the TDWR is a Cband radar, it also hydrometeor types, such as rain, hail, and snow, provides, in the near term, a source for the high for example (e.g., Ryzhkov et al. 2005). This upgrade will also include precipitation estimation

WHAT IS TO ADDRESS WHY NEEDED WHAT PROBLEM

There is a significant difference in the damage resulting from small vs. large hail driven by 60-70 Need to know whether hail is mph winds. The large hail is a bigger threat to life present and how big it is; need to and property. Also, some hail damage can be know the distribution of types and avoided by actions such as moving vehicles into sizes of hydrometeors in general garages. Precipitation type, size, Need to know how much rain Current radars have only two Z-R relations but weather processes are clearly more complex than distribution, has fallen; the two Z-R relationships are inadequate that: Radar estimates of precipitation are usually and intensity inaccurate.

Need to know onset, type, Winter storms have significant and widespread intensity, and total impacts. Some areas do not typically see much precipitation in winter winter precipitation, so are significantly affected by even small amounts of winter precipitation.

Figure 4: Like Figure 1, except these are issues related to inaccurate information about precipitation. algorithms that statistically show improvements in change is on the horizon: dual polarization accuracy of rainfall rates and amounts technology will likely be deployed beginning in (Giangrande and Ryzhkov 2008). 2010. In summary, while PAR technology will not Nine meteorologists from two key directly fix every radar deficiency in the WSR88D, stakeholder groups in the Southern Plains, NWS its adaptive scanning capabilities have strong forecasters and TV broadcasters, were potential to address the need for reliable, clean, interviewed for this study using the critical incident and accurate data without user intervention. The technique. Through focusing interviews around inherent rapid scanning capabilities of PAR could critical incidents, specific information was attained also provide the hightemporal resolution data about current radar capabilities and how those needed to better identify and monitor fast evolving capabilities helped or hindered participants' ability precursors of hazardous weather. If, as a to fulfill their roles. The incidents revealed specific, community, we decide to take advantage of PAR underlying problems behind participants' needs in capabilities, the other stakeholder needs found in weather radar. this study could be addressed through the The stories told by our participants development of dualpolarization PAR technology, illustrated why there are still issues with the radar and the implementation of radars with the and radarderived information meteorologists wavelengths and network density needed to needed to do their jobs. Forecasters spent much provide more consistent, lowelevation coverage. of their interviews describing how weather radar played—or could play—a critical role to help them 7. SUMMARY make the most of the science to create the best forecasts and warnings. Broadcasters spent much This study is a first interaction with users of their interviews illustrating where and how to provide the kind of information needed for station radars added critical information that decisionmaking during early developmental helped them narrow down and specify weather stages of radar technologies new to meteorology. threats to viewers. The resulting portrayal of the As Morss et al. (2005) point out, this process must needs of these two groups was intertwined. Both become iterative throughout the development if have very similar and complementary needs that the resulting system is to best meet the parallel their selfdefined roles. Forecasters focus information needs of users. This study explores more on the science with an eye toward user experiences with the current state of communication, whereas broadcasters focus more operational technologies and the current state of on communication with attention also paid to the the science. That background condition will science. change, especially if WSR88D replacement is a The problems participants spoke of fell 20year development process. An immediate into four basic needs. First, meteorologists clearly

conveyed the need for reliable, clean, and comments when we recently discussed this work accurate radar data. Because both groups have with them. intensive responsibilities during hazardous This work was prepared by the authors weather situations, they need to attain high quality with funding provided by NOAA/Office of Oceanic radar data without their intervention. Second, and Atmospheric Research under NOAA several stories involved weather situations that University of Oklahoma Cooperative Agreement evolved more rapidly and on smaller spatial scales #NA17RJ1227, U.S. Department of Commerce, than WSR88D can sample. Third, both groups and National Science Foundation Grant No. ATM told stories illustrating advantages of high 0648566. The statements, findings, conclusions, resolution and lowaltitude station or TDWR radar and recommendations are those of the author(s) data, and how the lack of that information in other and do not necessarily reflect the views of NOAA, areas hampered their awareness of the weather the U.S. Department of Commerce, or the National that was occurring. Finally, size, distribution and Science Foundation. type of hydrometeors in both warm and cold season events were critical information 9. REFERENCES participants could only partially infer in data from current radar systems. For example, both groups Boyatzis, R.E., 1998: Transforming Qualitative told stories where rainfall estimates were only Information: Thematic Analysis and Code qualitatively useful, and where radar data Development. Sage Publications, 184 pp. indicated large hail that was never reported. These four needs are informative to radar Crum, T. D., R. E. Saffle, and J. W. Wilson, 1998: developments currently underway. They indicate An update on the NEXRAD program and potential design requirements for both the future WSR88D support to operations. Wea. technology and the network configuration. The Forecasting , 13 , 253–262. adaptive scanning capability of PAR technology can provide optimized scanning strategies with Doswell III, C., A. R. Moller, and H. Brooks, 1999: PRFs and rainfall estimation algorithms Storm spotting and public awareness since the appropriate to the current weather situation(s). first tornado forecasts of 1948. Weather and The complementary fast scanning capability of Forecasting , 14, 544557. PAR technology could also provide the high temporal resolution data needed to better identify Dunn, W.R. and D.D. Hamilton, 1986. The critical and monitor fast evolving precursors of hazardous incident technique: a brief guide. Medical weather. The need for consistent and lowaltitude Teacher, 22 , 207–215. weather radar information could be partly met by a denser radar network. The fourth need for Drobot, S., 2007: Evaluation of Winter Storm comprehensive hydrometeor information is already Warnings: A Case Study of the Colorado Front being addressed by the planned upgrade of the Range December 2021, 2006, Winter Storm. WSR88D network to dualpolarization capability. Natural Hazards Center Quick Response If the dualpolarization upgrade results in the Report No. QR192, 8 pp. [Available from: significant service improvements anticipated, an http://www.colorado.edu/hazards/research/qr/ iteration of this type of study would reveal qr192/QR192.pdf ] whether—and why—this capability must be maintained in any new radar system or family of Flanagan J.C., 1954: The Critical Incident systems. Technique. Psychological Bulletin , 51 , 327– 359. 8. ACKNOWLEDGMENTS Giangrande, S.E., and A.V. Ryzhkov, 2008: The authors are grateful for the time our Estimation of rainfall based on the results of participants were able to spend with us and for polarimetric echo classification. J. Appl. their willingness to provide insight on their Meteor. Climatol. , 47 , 2445–2462. important roles. We also thank the 7 October 2008 attendees of the Experimental Warning Gibbs, G.R., 2002: Qualitative Data Analysis: Program Brown Bag Lunch for their helpful Explorations with NVivo. Open University Press, 257 pp.

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