2 We explain to each other Introduction - 1That which we don’t understandWe explain to each other
3 Introduction - 2 Low Level Wind Shear (WS) occurs frequently Can be overlooked when composing a TAF
4 Goal of Presentation Refresher Maintain/Heighten awareness of WS Encourage application in aviation forecasting
5 Some Questions Associated with WS What is WS?When should WS be the TAF?When should WS NOT be The TAF?When should a WS forecast be withdrawn?
6 Define WSA change in horizontal (or vertical) wind speed and/or direction with distance (or height). (Badner)A Vector Difference composed of wind speed/direction (NWS)
7 Two Types of WS: Convective WS Non-Convective WS Could also be ‘Micro-burst’ type of windsCan not be labeled as ‘WS’ in TAFNon-Convective WSMechanicalIdentified as ‘WS’ in TAF
8 Define WSWS in this presentation refers to “Non-Convective” Low Level Wind Shear.
9 Define WS (continued)In order to be “Low Level”, it must occur at or below 2,000 ft AGL.
10 When is it Low Level ‘Turbc’ and not WS? When strong, low-level winds mix down to the surface,The difference between surface and low-level winds minimal,Gives rise to Low Level Turbulence, not WS.
11 How does WS impact airline flight operations? “Compression” is a term used to describe what happens when the aircraft in front begins to slow down.As it slows, following aircraft begin to catch up.Much like cars approaching a stop sign.
12 How does WS impact airline flight operations? “Compression” occurs normally,but is enhanced by wind shear that slows landing traffic even more.This creates a ‘ripple effect’ that impacts other incoming flights.Correct forecasts can help flight planningSaving Timeand Money.
13 What are some SPECIFIC criteria for WS? “Strong” Pressure GradientsExpect WS If :Pressure gradients support winds of 40 kts or more,And surface winds are ‘light’
14 What are some SPECIFIC criteria for WS? Winds of 40 kts or more within 2,000 ft AGL, will give turbulence any time, butif surface wind is light, then expect WS.Need speed/direction differences to get WSOtherwise, it is low level turbulence.
15 Examples of “Strong” Pressure Gradients A PDX-BLI gradient of 8 mbs or more (measured or forecast)South to NorthTwice that if North to SouthA SEA-EAT gradient of -11 mbs or moreEast to West
16 NWP Products Surface Progs ‘Strong’ gradients are often ‘under forecast’ in prog runs.
17 NWP Products Numerical Guidance Products such as FRHTxx and FRHxx give Surface pressure forecastsBoundary layer wind forecastsIn need of Broad interpretation
18 Observations - These are NOT Forecasts! ROABsPIREPsACARs SoundingsSurface analysisNot always timelyMETARsVAD profile
19 What are some SPECIFIC criteria for WS? WSR-88D VAD profile:Light winds in METAR and 40 kts or more at VAD 2,000 ft wind.Winds differences of 60 degrees or more between METAR and VAD 2,000 ft wind.
20 WSR-88D VAD Wind Profiles 2,000 ft1,000 ftMETAR Z … KT…
21 WSR-88D VAD Wind Profiles Generally good for SEA, however,Lower level winds are affected by flow through the Strait of Juan De Fuca so don’t always represent conditions over SEA.East winds over the airport do not always displayed in VAD.
22 WSR-88D VAD Wind Profiles Generally good for SEA, however,Often usable for ATX, but not all sites.(MSX’s WSR-88D is on mountain and VAD winds begin at 9,000, so not usable for low level winds.)
29 Review of Main Points - 1Become aware of WS and the need to include in TAFs.Use meteorology, FORECAST WS when conditions are favorable.
30 Review of Main Points - 2 The TAF is a FORECAST not an Observation so, If conditions are favorable, don’t wait for PIREPs of WS before putting WS in TAF.
31 Quiz Time ! ! ! !If WS is mentioned in the AIRMET for your area of concern,Should you mention it in a TAF in that area when conditions are favorable?Should you mention it in a TWEB in that area?
32 Quiz Time ! ! ! !If you have WS in a TAF, and need to amend for a different reason,What criteria would you use to drop WS from the amended TAF?
33 Quiz Time ! ! ! ! How is WS encoded in the TAF? WShwshwshws/dddffKT WS = Non-Convective Wind Shearhwshwshws = Ht of shear in 100’s of ftddd = Directionff = Speed
34 Quiz Time ! ! ! ! How is WS encoded in the TAF? WS group follows the cloud forecast group.Remains in the forecast until the next ‘FM’ or the end of the forecast period if no ‘FM’ group follows.
35 Quiz Time ! ! ! ! In which groups can WS be included? The initial forecast group andThe ‘FM’ group
36 Quiz Time ! ! ! ! In which groups can WS NOT be included? BECMG TEMPO PROB
37 Quiz Time ! ! ! ! How is CONVECTIVE WS encoded in the TAF? You tell me…
38 Summary WS has large impact on aviation Forecasters Affects air traffic safety, flow, and comfortOccurs more often than is forecastForecastersMust become more aware of WSShould not be reluctant to include WS in TAFs when conditions warrant.
39 BibliographyJulius Bander, “Low-Level Wind Shear: a Critical Review”, NOAA Tech. Memo. NWS FCST-23, Apr 1979, reprinted Feb 1989NWS “Weather Service Operations Manual” , (WSOM) Chapter D-31, Issuance No. 97-5, June 6, 1997,
40 They don’t Like Surprises !! What the* % ~ # ??