P2.19 OBSERVATIONS OF INFLOW FEEDER CLOUDS AND THEIR RELATION TO SEVERE THUNDERSTORMS Rebecca J. Mazur1, John F. Weaver2,3, Thomas H. Vonder Haar2 1Department of Atmospheric Science, Colorado State University, Fort Collins, CO 2Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO 3 NOAA/NESDIS/RAMM Team,CIRA/CSU, Fort Collins, CO 1. INTRODUCTION tornadoes), and how the storms(s) will Organized lines of cumulus towers propagate. In particular, storm scale cloud within the inflow region of strong thunderstorms features on the order of 1-10 km are resolved on have been observed on satellite imagery 1 km visible satellite imagery. These features (Weaver and Lindsey 2004; Weaver et al. 1994). (e.g. feeder clouds and flanking lines) have been These cumulus lines have been labeled inflow studied using satellite imagery much less than feeder clouds, or simply feeder clouds (Fig. 1). other synoptic and mesoscale features, but often The relationship between feeder clouds and times are observed to be just as influential in storm development and intensification has not storm evolution (Lemon 1976; Weaver and been addressed extensively in the literature, nor Lindsey 2004; Weaver and Purdom 1995; has the occurrence of feeder clouds been Weaver et al. 1994). objectively linked to severe weather1. However, Another observing system that produces understanding how feeder clouds relate to high resolution observations of thunderstorms is severe weather could have positive implications the Weather Surveillance Radar-88 Doppler in severe storms forecasting and may add new (WSR-88D). Radar imagery taken from this insight into severe storm morphology. This system is heavily relied upon during warning study represents a first look at the relationship operations to diagnose storm characteristics between their occurrence and severe weather. such as strength, size, and motion (Moller Prediction of severe thunderstorms is 2001). In particular, the Mesocyclone Detection complex since many interacting weather Algorithm (hereafter MDA; Stumpf et at. 1998) is features both in the mesoscale and synoptic an automated radar algorithm that is used during scales create an environment conducive to severe weather situations to identify storms that severe thunderstorm formation and have mesocyclones. Stumpf et al. (1998) found intensification (Atkins et al. 1998; Klemp et al. that 90% of storms in which mesocyclones were 1981; Lemon and Doswell 1979; Purdom 1986; detected produced severe weather; therefore it Weaver et al. 1994; Weaver and Purdom 1995; is important to identify storms with Weckwerth 2000; Weckwerth et al. 1996, Wilson mesocyclones during severe weather warning et al. 1992). Meteorological observing systems operations. such as surface and upper air observations do The MDA is currently run during real- not resolve thunderstorms well since time operations in all US National Weather thunderstorms are considered sub-grid scale Service Forecast Offices. It displays information features on these observing networks. With about a mesocyclone’s strength and size so that satellite data, many observations of the the forecaster can make an informed decision atmosphere can be examined simultaneously to on whether the storm will produce severe identify where a thunderstorm or group of weather. However, detecting tornadic and/or thunderstorms will form, what factors will affect severe thunderstorms by identifying the evolution of the storm(s), what type of mesocyclones in radar data is very difficult to do severe weather will occur (wind, hail, and/or with great skill. Thus it would be advantageous to develop supplementary methodologies to the 1 MDA that could confirm questionable Defined by the National Weather Service as hail > 0.75 in. mesocyclones as well as provide information on in diameter, winds > 58mph (50kt), and/or tornadoes. the near storm environment to help assess the * Corresponding Author Address: Rebecca J. Mazur, Dept. likelihood that such storms will strengthen and of Atmospheric Sciences, Colorado State University, Fort become severe. Satellite imagery is the ideal Collins, CO 80523. email: [email protected] candidate for this role. Since the MDA is utilized during warning cloud streets, etc.). A McIDAS2 display system operations, it is suggested that adding served as the visualization tool for displaying the information from visible satellite imagery (i.e. imagery for this study. feeder cloud signatures) to the mesocyclone Although visible imagery is useful in detection process might improve a forecaster’s studying exterior storm scale features, the actual success in identifying and warning for severe core of the storm cannot be observed by the storms. Although feeder clouds are not well GOES Imager. Observations of the storm core understood in relation to thunderstorm are available in three dimensions using the development, Weaver and Lindsey (2004) WSR-88D weather radar. In particular, the radial suggest that feeder clouds may be a signal to velocity product of the WSR-88D measures the rapid intensification in a storm and also may be averaged particle velocities in a beam volume an indication that a storm will soon produce toward and away from the radar and is used to severe weather. Therefore, this study will take a detect areas of high wind and rotation in a storm first look at whether a relationship does exist (Burgess 1976; Moller 2001; Stumpf et al. 1998; between the occurrence of feeder clouds and Wood et al. 1996). Identifying rotation in a storm severe weather in a thunderstorm by is important since storms with areas of strong establishing a time correlation between the two cyclonic rotation, called mesocyclones, are likely storm features. Also, feeder cloud signatures to producing severe weather (Burgess 1976; will be compared to mesocyclone detections Burgess et al. 1979; Jones et al. 2004; Lemon et from the MDA as predictors of severe weather. al. 1977; Mitchell et al. 1998; and Stumpf et al. By establishing a correlation between feeder 1998). cloud signatures, mesocyclone detections, and The Mesocyclone Detection Algorithm severe weather, we hope to find some new (MDA) is an automated algorithm used in insight into feeder cloud development and operational forecasting to identify circulations in thunderstorm intensification as well as improve storms that are mesocyclones. The MDA is forecasting of severe weather. used to assist the user in diagnosing which mesocyclones are more likely to represent a 2. DATA SOURCES threat. Characteristics of the mesocyclone such Feeder clouds can be observed using as strength and size which may not be obvious imagery from GOES Imager channel 1. Channel to a human observer can be sampled using the 1 collects radiation in the visible spectrum MDA. Not all thunderstorms that produce severe centered on .65µ at 1 km. Images can be taken weather have mesocyclones, but those storms during normal scanning operations and rapid with mesocyclones have a higher chance of scan operations (RSO). RSO images are taken producing hazardous weather and the MDA can over the continental US at intervals that vary to be useful in identifying these storms. include 5, 7, 10, and 12 minutes (Kidder and For this study, MDA data for a subset of Vonder Haar 1995). Normal scanning operations 9 of the 24 case study days were analyzed using take images every 15 minutes and a four-times CIRA’s research AWIPS. Even though only a daily full-disk scan that requires 30 minutes. subset of radar data were analyzed compared to GOES-8 and 9 were the predecessors satellite data, if combining the two data systems of the current GOES systems (10 and 12) and will add any value to the severe weather provided similar data as 10 and 12. For this prediction process, we should expect some study, visible imagery from all four satellites indication of that fact using our case data. taken in RSO and normal scanning operations was examined for 24 days on which severe 3. FEEDER CLOUDS weather occurred. The purpose here is to Feeder clouds are small scale lines of observe how feeder clouds evolve in a storm cumulus towers that seem to occur most often in and identify whether any relationship can be supercell thunderstorms. They are positioned established between these cloud features and ahead of the flanking line in the inflow region of severe weather. RSO is useful during severe a storm and are oriented roughly 45°-135° to the weather situations when environmental changes storm motion. Fig. 2 illustrates the proximity of occur rapidly and animated loops can be used to highlight cloud features that are persistent over 2 time (i.e. growing storms, overshooting tops, The Man computer Interactive Data Access System (McIDAS) is a suite of applications for displaying and analyzing meteorological data. feeder clouds to a thunderstorm’s anvil and around 2015 UTC on a north-south oriented flanking line. Feeder clouds can be 5-50 km long dryline. As the towers organized and moved and 5-10 km wide, and resemble horizontal eastward, the storm rapidly intensified, and convective rolls (HCR; having alternating storm splitting could be seen on radar beginning clouds/no clouds co-located with regions of at 2116 UTC (not shown). By 2125 UTC, a upward and downward motion, respectively). large OST had formed and a mesocyclone was They are a steady feature relative to the storm, detected by the KTLX radar. joining the “rain-free” updraft on its eastern edge The 2132 UTC visible satellite image (Weaver et al. 1994). (Fig. 3a) shows a large OST with an anvil The mechanism(s) that initiate feeder spreading from the updraft. This indicates that clouds are unknown, but it seems that they form an intense updraft was developing although no as a thunderstorm is rapidly intensifying. mesocyclone was detected in the updraft region Oftentimes, feeder clouds will appear on visible (Fig. 4d). The mesocyclone detected on the imagery following an enhancement of the north flank was likely associated with the storm overshooting top (OST).