Thunderstorm Consistency Guidance
To ensure consistency between the TAF and the Collaborative Convective Forecast Product (CCFP), forecasters will use the following criteria when creating their TAFs.
For a FAA-Core Airport:
- When the CCFP forecast thunderstorms with high confidence level AND medium coverage (or greater) at the TAF location, thunderstorms (TS) should be included in a "TEMPO" or "PROB30" group. [Note: "TEMPO" can be used during the first 9 hours and "PROB30" for the later periods]
- When the CCFP forecasts high confidence AND/OR high coverage, thunderstorms (TS) should be forecast as prevailing conditions or a "TEMPO" group.
Note: FAA-Core Airports are airports that are significant to the national air transportation system based on air traffic operations and passenger boardings. There are approximately 30 core airports.
For Non-Core Airports: Although not required, it is recommended that you apply the above criteria for consistency.
Public Forecasts and TAF Consistency
When a NWS public forecast has a 60 percent chance (or greater) of thunderstorms which includes a TAF site, then thunderstorms should be included in the TAF.
This is going to be a judgment call as to how and when you include thunderstorms (TS) in your TAF. After going through your forecast analysis process, it comes down to your confidence level in the convection occurring and how widespread you think it will be.
- Do you anticipate the convection to organize into a line or large convective system?
- Do you anticipate thunderstorms to be more scattered over the area?
- Does your confidence level change due to the uncertainty of the event in the later time periods?
More emphasis and detail should be included in the first 12 hours of the TAF. If your confidence level is "high" that thunderstorms will occur particularly during the first 12 hours, then your TAF would likely include "TS" as a prevailing condition or use a "TEMPO" group.
In later time periods when your confidence level is lower and there is uncertainty to the type of convection, then you might use a "PROB30" or "VCTS" to indicate the threat of thunderstorms.
It is recommended you do not use "TEMPO" groups the last 6 hours of your forecasts.