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It's All in How You Look at It NEXRAD Now January 2010 Issue 19 It’s All in How You Look at It Late evening and early morning returned data derive target velocities. What’s severe thunderstorms in eastern Min- The more orthogonal to the beam nesota demonstrated the importance of radial that the target motion is, the less Inside? viewing angle in Doppler measure- of a target velocity component the Page 4 ment. The location and the motion Solar Flux Resources of these storms relative to the WSR-88D made them a challenge Page 5 for radar interrogation by warning Operational “Tid Bits” forecasters at WFO Twin Cities/ Page 7 Chanhassen (KMPX). ROC Stars In the two events of interest, there was a pair of Doppler radars Page 8 at nearly identical distances from The Importance of the storms. One was the WSR-88D Proper Clutter Filtering at WFO KMPX while the other Page 13 was TMSP, an FAA Terminal Dop- NWS VCP Usage pler Weather Radar (TDWR) that Survey assists operations at the Minneapo- lis/St. Paul International Airport. Figure 1: 10:28pm CDT August 4, 2009 Page 17 Wind Farms and the These radars are located 30 miles KMPX reflectivity with radar distances WSR-88D: An Update apart from one another. and storm motion vector. While the radars were at a sim- Page 22 Lowest Beam Center Heights ilar proximity from the storms and WSR-88D Electronic of Velocity Data of Interest on August 4 the heights of the lowest beam Technical Manual centers were quite comparable, the KMPX 2,300 ft Distribution output velocity data was markedly TMSP 3,300 ft Page 23 different. This was a direct result Scenic RDA Photo of the nearly 90° angle that the Table 1 Contest Winners KMPX pulses intersected the storm paths. The Doppler radar radar receiver can measure. This was Page 30 Researching receiver can detect phase shifts in the the case for the KMPX WSR-88D WSR-88D Parts pulses that strike targets, and from that Continued on Page 2 NEXRAD Now Look at It Continued from Page 1 during these two events. Near 10:30pm CDT on August 4, 2009 an organized thunderstorm north of the Twin Cities was evolving east southeast. This had no history of being severe, but the reflectivity revealed morphol- ogy into a poten- Figure 2: August 4, 2009 Doppler radar data comparison of the lowest angles from KMPX and TMSP. tial wind threat. There was little in the way of automated observations in the area of the storm, so accurate Doppler data was essen- tial. Seen in Figure 1, the WSR-88D radar was at a disad- vantage in measuring velocity due to the storm motion vector. The angle between the measuring radials and the storm motion was a nearly orthogonal 84° at warning deci- sion time. On the other hand, TMSP’s radials crossed the storm motion vector at a considerably less angle of 37°, which actually improved to 27° later in the storm’s life cycle. Thus a much larger component of storm motion was measurable by TMSP, and accordingly more realistic Dop- pler data was output. From Table 1, one can see that the lowest beam height from each radar was within only a few thousand feet of the Figure 3: 6:28am CDT August 5, 2009 ground, potentially offering a more accurate indication of KMPX reflectivity with radar distances and the winds realized at the surface. The lowest level base storm motion vector. velocity data from near the time of this event’s Severe Thunderstorm Warning issuance can be seen in Figure 2. Lowest Beam Center Heights Just over a 20 kt difference existed in the maximum veloc- of Velocity Data of Interest on August 25 ity bin data within the storm as a direct result of the radial KMPX 1,200 ft angles versus the storm motion. Warning forecasters that TMSP 1,550 ft evening recognized this discrepancy given this storm this Continued on Page 3 Table 2 page 2 NEXRAD Now Look at It Continued from Page 2 orthogonally met the target motion vectors. Some discrepancy given this storm location and its of the radials with the greatest amount of gray motion. As a result, TMSP was the radar favored shade are those cutting through the high velocity area of the storm, highlighting the problem. This storm would soon produce a measured 58 mph gust, as well as, take down several large trees. These two August events from eastern Minnesota reflect how critical it is for operational WFO staff to keep in mind their radar Figure 4: August 25, 2009 Doppler radar data comparison of the lowest angle from KMPX and TMSP. viewing angles rela- tive to the storm for more representative velocity data. The warning during an event and utilize available resources. The was issued ahead of destructive winds that brought zero or near-zero isodop in velocity data can high- down dozens of large trees near the community of light radials where perpendicular storm motion Wyoming. may cause challenges. Within the WFO Advanced Three weeks later, another thunderstorm at an Weather Inter- almost identical line of longitude led to a very sim- active Process- ilar observation. On August 25th, an early morning ing System area of storms was moving across the north metro (AWIPS) there of the Twin Cities. Figure 3 depicts how this is an Esti- storm was closer to the radar than the first case, but mated Actual the geometry of it was just as challenging for the Velocity (EAV) KMPX radar because of the east southeast storm tool that can motion. calculate the As seen in Figure 4, the velocity magnitudes on target motion TMSP were once again higher, but even more component of appreciable in this case. The interpreted near zero measured base Figure 5: TMSP lowest level base velocities are in the gray colors on the KMPX velocity. The velocity data with AWIPS EAV tool image. Because the echoes were in reality moving, user-provided output from the Aug. 5th severe thunderstorm warning (outlined in this area basically highlights where the radial variable is sim- yellow) event. Continued on Page 4 page 3 NEXRAD Now Solar Flux Resources Look at It Each morning, WSR-88D maintainers around the country Continued from Page 3 call the Space Weather Prediction Center (SWPC) requesting the ply the motion of the storm of interest. 10.7cm solar flux values (observed and forecast). This tool will only provide output As a former WSR-88D operator and instructor at Keesler however if the angle of intersection AFB, I wanted to inform the radar maintainers they can also between the radial and storm motion obtain the flux measurements from the SWPC web site and via is less than 75°. In the two scenarios email. above, the EAV tool provided no out- Section IV of the Joint USAF/NOAA Report of Solar and put for the KMPX radar for that very Geophysical Activity, available at http://www.swpc.noaa.gov/ reason. It did though further help esti- forecast.html, provides the observed 10.7cm flux, as well as, a mate the TMSP measured winds. In 3-day forecast. Figures 2 and 4, the TMSP maximum These forecasts, along with space weather alerts of potential velocity estimated by the EAV tool interest to radar maintainers, can be received via email by sub- was 68 kts for the August 4th event scription at https://pss.swpc.noaa.gov/LoginWebForm.aspx? (Figure 5) and 63 kts for the August ReturnUrl=%2fproductsubscriptionservice%2fMainMenuWeb th Form.aspx. 25 event. This tool may allow for Finally, SWPC plans to introduce a menu-driven phone more direct correlation of measured answering system within the year. One option will be dedicated data and observed speeds or wind to providing current and forecast 10.7cm flux values. damage for warning forecasters and damage survey teams. Rob Steenburgh, SMSgt, USAF AF Liaison to SWPC Matthew Friedlein Twin Cities/Chanhassen WFO NEXRAD Now is an informational publication of the WSR-88D Radar Operations Center (ROC). We encourage our readers to submit articles for publication. Please email all articles and comments to: [email protected] All previous issues of NEXRAD Now can be viewed on the ROC Home Page at: http://www.roc.noaa.gov/WSR88D/NNOW/NNOW.aspx Director.............Richard Vogt Deputy Director...Terry Clark Editor.................Ruth Jackson page 4 NEXRAD Now Operational “Tid Bits” Terminal Doppler Weather Radar (TDWR) NCDC WSR-88D Archives and Display Tools Data Flow The National Oceanic and Atmospheric Admin- Several Weather Forecast Offices (WFOs) have istration’s (NOAA) National Climatic Data Center experienced frustration with extended TDWR out- (NCDC) is an on-line and no-charge source for all ages and having the outages addressed in a timely the centrally collected TDWR (all 45 operational manner. The Radar Operations Center (ROC) rec- sites) and WSR-88D (155 sites) products (http:// ommends that the availability of TDWR data be www.nws.noaa.govtgrpccds_radar_products.pdf). checked during shift changes. If there is an outage, In addition, NCDC archives the Level II data from the first call should be to the applicable Federal 137 WSR-88Ds and has hourly NEXRAD national Aviation Administration (FAA) mosaics. Find inventories of archived radar data Maintenance Operations Control at: http://www.ncdc.noaa.gov/ Center (MOCC). If the MOCC nexradinv/choosesite.jsp. Data cannot find or correct the issue, call ordered is sent to an FTP site for the WSR-88D Hotline for assis- retrieval in usually less than an hour – tance. The ROC will begin deploy- depending on the amount of data ment in late January 2010 of a requested.
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