AFWA T1 Method
The T1 Method for determining the speed of the maximum convective wind gust is as follows:
- Compute the dry stability index T1. There are 2 ways by which to compute T1:
- With an inversion, the top of which is no more than 150-200 hPa above
the surface, go up a moist adiabat from the surface to 600 hPa and note
the temperature. Subtract the 600-hPa dry bulb temperature from this value
to get T1.
- With no inversion or an inversion more than 200 hPa above the surface, compute maximum temperature TMAX by going dry adiabatically from the 850-hPa temperature to the surface. From this surface temperature, proceed up moist adiabatically to 600 hPa. Subtract the 600-hPa dry bulb temperature from this valued to get T1.
- Compute the maximum wind gust V1, using the formula V1=13*sqrt (T1). This will yield the speed of maximum wind gust in knots.
Estimate the direction of the mean wind in the layer between 10,000 and
14,000 feet AGL. This will be the forecast wind direction of the computed gust.