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The Down-Low on Wind Shear

There are some things your CFI may not have taught you from the TAF.

TAFs are one way to identify the likelihood of nonconvective low-level wind shear for your departure or destination airport. [Adobe Stock]
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Key Takeaways:

  • Nonconvective low-level wind shear (LLWS) in Terminal Aerodrome Forecasts (TAFs) indicates a rapid increase in wind speed with height below 2,000 feet, a condition often misunderstood by pilots as turbulence, though the air is frequently smooth.
  • This phenomenon is primarily caused by atmospheric stability, particularly temperature inversions, which prevent vertical mixing and allow a "low-level jet" of faster air to flow above surface friction.
  • While often a non-event, nonconvective LLWS is significant for pilots operating from high-density altitude airports, balloon pilots, and especially when combined with moderate to heavy rain, as it can contribute to hazardous wet microbursts or downbursts.
  • Nonconvective LLWS forecasts are found in TAFs (coded as WS020/15055KT, for example) and graphical AIRMETs (G-AIRMETs), providing crucial preflight weather information.
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There’s no doubt that terminal aerodrome forecasts, simply known as TAFs, are perhaps the most detailed aviation forecasts available to a pilot. Within them lays a piece of forecasting critical to understand, and that’s for low-level wind shear.

If you call Flight Service for a standard briefing or get an automated briefing through one of the many heavy-weight apps, you can bet the farm that any TAFs along your proposed route and at your departure and destination airports will be a part of this briefing. There are, however, some finer details about the forecast found in TAFs that instructors fail to pass along to their primary students possibly owing to their own lack of knowledge. The top one on the list includes a forecast for nonconvective low-level wind shear (LLWS).

Scott Dennstaedt, Ph.D

Scott resides in Charlotte, North Carolina, and flies regularly throughout the Mid-Atlantic and Southeast U.S. He is a CFI and former NWS meteorologist. Scott is the author of "The Skew-T log (p) and Me: A Primer for Pilots" and the founder of EZWxBrief.

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