Page 33 - Volume 15 Number 8

sized hail throughout my yard. If you based your decision to fly to Charlotte solely on the 1200 UTC TAF, you might have been a bit surprised if not annoyed having to work your way around these thunderstorms since you were only expecting some high-based rain showers in the vicinity of the airport. And yes, the TAF went through several amendments including this one at 1642 UTC...
FM271700 26008G18KT 6SM -SHRA BR BKN045 OVC070CB
...and this one at 1739 UTC...
TEMPO 2718/2720 25010G20KT 5SM -TSRA BR SCT030 OVC050CB
This last amendment was issued just 34 minutes before the thunderstorm entered the Charlotte terminal area. While you may think the forecaster produced an inferior forecast, don’t be so quick to make judgments until you’ve walked a mile in his or her shoes. Imagine
trying to forecast the weather for just your immediate neighborhood. From a forecast perspective it’s inconsequential what happens in the town or neighborhood next to yours.
For airports that have commercial operations, forecasters have a whole different set of outside pressures. This is especially true for high- impact airports such as Charlotte/ Douglas. When a forecaster includes TSRA as the prevailing condition or it is included in a TEMPO group, airlines landing at this airport during this time must file an alternate which implies that they must carry additional fuel to reach that alternate. So, forecasters are extra sensitive when placing a forecast for thunderstorms in the terminal area when there’s very little confidence. Of course the goal between the NWS and the airlines is to balance economics and safety.
Despite these outside pressures, TAFs have real limitations due to
the extremely small size of the
terminal area. If you are looking
at the TAFs the night before your
flight, you should not depend on
them alone to highlight areas
of convection for the next day.
Forecasters are potentially decades
away from being able to do this with
any degree of accuracy. Depending
on the circumstance, forecasting
thunderstorms in that five-statute
mile terminal area is either
incredibly difficult or fundamentally
impossible more than a few
hours in advance. Meteorologists
can look at all the available data,
with all the available scientific
in their terminal forecast. T&T •
understanding, and still be way off
Scott C. Dennstaedt is a CFI and former NWS research me- teorologist. To learn more about aviation weather you can visit his website at http://avwxwork- shops.com.
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TWIN & TURBINE • 31