Echo TopsPrecipitation EstimatesPowerPoint PresentationPrecipitation EstimateInterpreting Doppler SignaturesAzimuth Resolution ConsiderationsThe Zero Isodop “Problem”Large Scale WindsSlide 9Example from KMKX 88DThe VAD Wind Profile (Velocity Azimuth Display)Small Scale Winds - Diffluence/Confluence -Small Scale Winds - Cyclonic Confluence/Diffluence -Small Scale Winds - Pure Cyclonic Rotation -Small Scale Velocity ExampleSmall Scale Velocity ExampleStorm Relative Velocity - SRV vs Base VelocitySRV vs. Base Velocity - strong rotation -SRV vs Base Velocity - subtle rotation -Slide 20SRV vs Base VelocitySRV vs Base Velocity - straight line winds -Bow EchoesReview Clear-Air RadarSlide 25Slide 26Clear-Air Wind ProfilersWind Profiler SpecificationsEcho TopsFairly accurate at depicting height of storm topsInaccurate data close to radar because there is no beam angle high enough to see tops. Often has stair-stepped appearance due to uneven sampling of data between elevation scans.Precipitation EstimatesStorm Total Precipitation●Total estimated accumulation for a set amount of time.●Resets storm total whenever there is no rain detected for an hour.-Updated once per volume scan.-Shows accumulated rainfall for the last hour.-Useful for determining rainfall rate of ongoing convection.One Hour Precipitation TotalPrecipitation EstimateAdvantages and Limitations●Great for scattered areas of rain where no rain gauges are located●Provides a graphical ‘map’ of rainfall for an entire region●Data can be overlaid with terrain and watersheds to predict reservoir and waterway crests●Estimates based on cloud water levels and not ground level rainfall●‘Hail Contamination’ causes highly inflated values●High terrain causes underestimates●Useful as a supplement, not replacement for ground truth informationInterpreting Doppler SignaturesDisplay examples provided by:National Weather Service Steve Davis - Lead ForecasterMilwaukee/Sullivan National Weather Service Forecast OfficeRange0120 nm(example)Weak inbound, weak outboundRotation too small to be resolvedStronger inbound than outboundStrong inbound, strong outboundAzimuth 3Azimuth 2Azimuth 1Enlarged image along a radial. Individual “blocks” represent one sample volume. This graphically shows the radar resolution.•closer a rotation the more likely it will be identified correctly •rotation smaller than the 0.50 beam width (possible at long ranges) > rotation is average of all velocities in sample volume•Previous 10 beam width improved by super-resolutionAzimuth Resolution ConsiderationsRotational couplet identification can be affected by azimuth resolution.100%100%0%0%When the wind velocity is parallel to the radial, the full component of the wind is measuredWhen the radial is perpendicular to wind direction, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”.What percentage of actual wind will the radar detect?00 = 100% - Parallel150 = 97%300 = 87%450 = 71%600 = 50%750 = 26%900 = 0% - PerpendicularThe Zero Isodop “Problem”Large Scale Winds“S” Shape“S” shape of the zero isodop indicates veering winds with height. Veering may imply warm air advection.The combination shape of the zero isodop indicates both veering and backing winds with height. CombinationBackward “S” ShapeBackward “S” shape of the zero isodop indicates backing winds with height. Backing may imply cold air advection.Use the Zero Isodop to assess the vertical wind profile.Large Scale WindsUniform FlowStraight Zero Isodop indicates uniform direction at all levels.Uniform Flow with Jet CoreStraight Zero Isodop indicates uniform direction at all levels >> inbound/outbound max’s show a jet core aloft with weaker winds above and below.Example from KMKX 88DLow level jet maxJanuary 5, 1994Steady snowfallThe VAD Wind Profile(Velocity Azimuth Display)Small Scale Winds- Diffluence/Confluence -DiffluenceOften seen at storm top level or near the ground at close range to a pulse type stormConfluence would show colors reversedSmall Scale Winds- Cyclonic Confluence/Diffluence -Anticyclonic confluence/ diffluence would show colors reversed in each panel.Cyclonic Confluence Cyclonic DiffluenceSmall Scale Winds- Pure Cyclonic Rotation -Pure Cyclonic RotationAnticyclonic rotation would show colors reversedSmall Scale Velocity ExampleSmall Scale Velocity Example Rotation with tornadoStorm Relative Velocity - SRVvsBase VelocitySRV: Subtract estimated velocity of thunderstorm from the Doppler radial velocity– Make the storm stationaryWhen diagnosing rotational characteristics, use SRVmotion of the storm masks subtle rotations within the stormWhen diagnosing Straight Line Winds (bow echo, microbursts), use Base Velocitystraight line winds are sum of the winds produced by the storms, plus storms movementSRV vs. Base Velocity- strong rotation - Storm Relative Velocity Base Velocityrotation in tornadic thunderstormSRV vs Base Velocity- subtle rotation -Base Velocity Storm Relative VelocityJanesville F2 tornado. June 25th, 1998 ~ 700 PMInteresting note: These scans are at 3.40 elevation. The 0.50 elevation showed little rotational information.SRV vs Base Velocity- subtle rotation -0.503.40Base Velocity Storm RelativeLittle/no rotation seen at lowest elevationSRV vs Base VelocityBase Velocity Storm Relative VelocitySRV vs Base Velocity- straight line winds -Base velocity shows max inbound winds of 55 to 60 kts.SRV shows max inbound winds of 30 to 40 kts.Bow EchoesDetecting and Predicting DownburstsoBow echoes are caused by severe downbursts, accelerating part of a line of thunderstorms ahead of the rest.oThe strongest downbursts occur under and just north of the apex of the bow, but can occur elsewhere toooSurface winds can exceed 70mph in strong bow echoes.oBow echoes can move at over 50 mph.oHighest reflectivities and strongest velocities are found at the apex.oLook for a tight gradient of reflectivity.Review Clear-Air RadarVHFUHF10 cm1/3l-4l-VHFUHF10 cm1/3l-4l-6 612Ni iin a=�2nCClear-Air Wind ProfilersWind Profiler SpecificationsFrequency (MHz)Wavelength (m)Maximum Altitude (km)Antenna Size (m)Target Band Designation50 6 20 100 x 100 Clear Air VHF449 0.75 15 15 x 15 Clear Air and Heavy PrecipitationUHF915 ~0.3 5-6 5 x 5 Clear Air and PrecipitationUHF1036 ~0.3 5.5-6 5 x 5 Clear Air and