Example of Terminal Digital Radar Weather Display (photo courtesy of AOPA) Introducing Revised ATC Terms for Describing Radar Weather Echoes to Pilots by Christine Soucy and Michael Lenz hen thunderstorm sea- “Z.”) The four terms will be used uni- determine the intensity (dBZ) of radar son begins this year, pi- versally in the National Airspace Sys- weather echoes and display that infor- lots will start hearing tem (NAS) by approach controllers mation to the controller. W some very important and Air Route Traffic Control Center Most of us are familiar with The changes in the way Air Traffic Control (ARTCC) and Automated Flight Ser- Weather Channel and local news and (ATC) describes radar weather echoes vice Station (AFSS) specialists. The weather broadcasts that use the to pilots. Beginning in late spring decision to stan- 2006, pilots will hear ATC use four dardize the termi- Figure 1 terms, “light,” “moderate,” “heavy,” nology was easy to and “extreme” to describe weather make because the ATC Weather dBZ radar echoes. Each term represents a ARTCC facilities precipitation intensity level paired with and many of the Radar Terms Reflectivity Levels a dBZ range (Figure 1) to help pilots terminal approach interpret the severity of the flight con- control facilities LIGHT < 30 dBZ(not available to ARTCC) ditions present. (A dBZ is a measure now have digital MODERATE 30 to 40 dBZ of radar reflectivity in the form of a log- radar display sys- HEAVY >40 to 50 dBZ arithmic power ratio [in decibels or dB] tems with proces- EXTREME >50 dBZ with respect to radar reflectivity factor sors that can better MARCH/APRIL 2006 27 Doppler NEXRAD (next genera- tion radar) WSR 88D weather radar. Some of you may even use those broadcasts to sup- plement your flight planning and overall weather awareness. However, there are significant differences with how weather information is displayed on a controller’s radarscope and the local news weather broadcast depictions. NEXRAD is de- signed to detect and display weather, but ATC radar sys- tems are designed to detect and display aircraft. Because the NEXRAD color coding and 16 individualized precipitation levels can provide excess clut- ter and possibly compromise the ability of controllers to safely perform their duties, dif- ferent systems for depicting weather radar echoes needed to be developed for the ATC environment. In air route traffic control centers, NEXRAD data is fed through the Weather And Radar Processor (WARP) that Figure 3 organizes the 16 NEXRAD lev- els into four reflectivity (dBZ) categories. (See Figure 1). Re- ARTCC Displaying both WARP/NEXRAD (color) and ARSSR (/////’s and HHHH’s) depicting moderate flectivity returns of less than 30 through extreme precipitation dBZ are classified as “LIGHT” and are filtered out of the center con- you can see in Figure 2, the ARTCC’s In the approach control world, nei- trollers’ display. The remaining three WARP system does not display dBZ ther NEXRAD nor WARP is available. categories correlate to bands of dBZ levels below 30, therefore center con- Instead, radar weather echoes are dis- values to assist pilots in evaluating the trollers will not be able to report areas played by the Airport Surveillance severity of flight conditions that might of “light” weather radar echoes. Radar (ASR) systems using Common be associated with those precipitation WARP/NEXRAD is a vast im- Automated Radar Terminal System returns. Therefore, the wide range of provement over the Air Route Surveil- (Common ARTS) or Standard Terminal color coding available to NEXRAD is lance Radar (ARSR) display of weather Automation Replacement System not available to the controller and, as radar echoes that center controllers (STARS) digital processors. The digi- used exclusively prior to tized ASR 9 and 11 systems (and Figure 2 the implementation of the some ASR 8 systems that have been NEXRAD type weather digitized) paired with a weather radars. The ARSR dis- processor, display the four weather ATC Weather plays the echoes to the radar echo intensity categories (see Radar Terms dBZ controller by indicating Figure 1) to the controller. Terminal fa- “moderate” intensities cilities can and do display “light” (less used in ARTCC Reflectivity Levels with a slash mark “/” than 30 dBZ) areas of precipitation. and more intense areas Of course, there are no absolutes. MODERATE 30 to 40 dBZ with the letter “H” (see In the universe of terminal radars, the HEAVY >40 to 50 dBZ Figure 3 for an example NAS still has a few non-digital ASR EXTREME >50 dBZ of an ARSR and WARP systems. While these systems do a display). good job of displaying weather radar 28 FAA Aviation News needed. The ARTCC WARP/NEXRAD updates every one to six minutes. Terminal (ASR based) systems show near “real time” echoes. • Make sure the controller under- stands what services you want. • Maintain situational awareness concerning your position and the weather areas you wish to avoid. • Include the information that you are on a heading assigned/ap- proved by ATC for weather avoidance, when you report onto the next controller’s fre- quency. • Verify what additional services ATC is providing to you. Is it what you need? PIPE UP WITH A PIREP! Precipitation echo depiction similar to non-digital ATC display - Intensity is unknown Pilot reports (PIREP) of flight con- echoes, they lack processors that can likely there is to be greater intensities ditions are an invaluable source of in- discern the intensity of the echoes. of precipitation; and when conditions formation for other pilots and con- These facilities will not be able to use are favorable for convective activity, trollers as well. PIREPs should include the terms, “light,” “moderate,” “heavy,” turbulence and other weather hazards reports of turbulence, icing, cloud tops or “extreme.” Controllers who work should be expected. As the intensity and bases, intensity of rain, presence from these displays will be able to tell of precipitation increases, so too, of hail, sleet, etc. A PIREP is often the pilots the position of weather radar does the likelihood of more severe only source of information regarding echoes but will state, “intensity un- weather conditions. Pilots should also actual flight conditions a pilot may en- known” because their system does remember that turbulence can be counter. Do your part for flight safety not indicate what dBZ level of reflectiv- present in areas where ATC does not and pipe up with a PIREP! ity is present. display precipitation at all. Therefore, In the world of ATC, weather radar pilots should always exercise care PIREP echoes are all referred to as “precipita- when transiting areas of known or REPORTING FORMAT tion” even though, technically, it is suspected convective activity. possible the echo could be associated Pilots of light general aviation air- For anyone who has never sub- with birds, volcanic ash, etc., or pre- craft should even approach areas of mitted a PIREP, the Aeronautical Infor- cipitation that is not reaching the “light” precipitation with caution. A mation Manual (AIM) explains how to Earth’s surface (virga). Controllers will rapidly growing thunderstorm can in- submit one, the uses of a PIREP, and tell pilots the location of significant crease at a rate of 6,000 feet per the format a pilot should use in report- areas of “precipitation” when it ap- minute! Think of the time-lapse pho- ing information. AIM paragraph 7-1- pears that it may affect the aircraft’s tographs and weather radar loops 21, Pilot Weather Reports, is the refer- flight path. They will also provide as- showing building thunderstorms. ence. Table 7-1-6, PIREP Element sistance in the form of course devia- “Light” precipitation could grow to Code Chart, explains the reporting for- tions when requested by the pilot. “moderate” and “heavy” levels within a mat with the elements explained. Rainfall rates (i.e., inches/hour) as very short period of time, given the they relate to intensity (dBZ) have not right conditions. The following tips are 5 been correlated with the ATC displays. offered to assist pilots in navigating Christine Soucy is with FAA’s Of- Therefore, the terms (light/moderate/ stormy skies safely. fice of Accident Investigation, Accident heavy/extreme) cannot be Coordination Branch and Michael equated/correlated to rates of rainfall • Request course deviations early. Lenz is a Program Analyst in Flight per se, at this time. Generally however, Don’t wait until the last moment. Standards’ General Aviation and Com- the more intense the echo, the more • Ask for information updates as mercial Division. MARCH/APRIL 2006 29.