It is not common knowledge for a pilot to know the specific organization or forecasters that generate the various aviation weather forecasts they use every day. This is certainly a point that is clearly not emphasized in any training curriculum used by flight schools and typically is not discussed in many aviation texts. Pilots are simply taught the basic characteristics of those forecasts and how to utilize them in the context of their preflight planning analysis. But it can be useful to know the source of the official forecasts and understand the challenges faced by these underappreciated meteorologists.
There are several official weather products that pilots use that are generated by human forecasters. These include area forecasts (FA), AIRMETs (WA), SIGMETs (WS), convective SIGMETs (WST) and terminal aerodrome forecasts. Terminal aerodrome forecasts, better known to pilots as TAFs are provided to pilots as part of a standard briefing. Despite what some pilots are taught, they are not automatically generated by a computer and are not issued by the staff at the Leidos (Flight Service). Leidos only reports the weather and forecasts and never issues any specific forecasts including TAFs.
With the exception of airports controlled by the military, TAFs are constructed by highly skilled meteorologists located at the local Weather Forecast Offices (WFOs). Each weather forecast office shown above has the responsibility of issuing the TAFs for one or more terminal areas the fall within their county warning area (CWA) with an average of roughly five or six per forecast office. For example, the Greenville-Spartanburg weather forecast office located in Greer, SC is responsible for issuing the TAFs for six airports that fall in their CWA. These include Anderson County Airport, Asheville Regional Airport, Charlotte/Douglas International Airport, Greenville Downtown Airport, Greenville-Spartanburg International Airport and Hickory Regional Airport as shown below.
Only a few forecasters at the local WFOs around the country are also pilots. However, they do understand how their forecast and subsequent amendments may impact a pilot’s preflight planning and decisions while en route. As a result, these meteorologists are highly motivated to provide as accurate of a forecast as possible within the constraints of the directives provided by the NWS.
A TAF is considered a point forecast and is not meant to be used as a zone or area forecast. Given this challenge, the local forecasters have the best chance to identify the wind, ceiling, visibility and weather that might occur at a specific airport over the next 24 or 30 hours (depending on the TAF site). To meet that challenge, each WFO identifies local forecast rules that will capture the effects of terrain (mountains, bodies of water, urban setting, etc.) as well as climatology. For example, a terminal area located within the city may have a much different forecast than one located 10 miles outside of the city. Also a terminal area next to a river may hold onto the fog a lot longer than a terminal area 10 miles away from the river.
Thunderstorms and fog represent some of the most difficult weather to forecast. The difference between a forecast of OVC001 and CLR is significant to a pilot, but in some circumstances the meteorologist may have conflicting guidance and often has to rely on their local knowledge to decide if that radiation fog will form in the early morning hours.
A widespread convective outbreak is normally very well forecast, but when the thunderstorms are expected to be more isolated or scattered, a forecaster will tend to leave out a chance of thunderstorms, knowing they may have to amend the forecast after the thunderstorms begin to develop. In some circumstances, it simply comes down to meteorological risk; they are hoping for the best without always forecasting the worst.
Most pilots are weatherwise, but some are otherwise™
Dr. Scott Dennstaedt
Weather Systems Engineer
CFI & former NWS meteorologist