Convection » Convective Wind Gusts 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. Depending on the inversion characteristics, T1 will be
computed in one of two ways:
- 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 surface temperature, TMAX, by going dry adiabatically from the 850-hPa temperature to the surface. From this surface temperature, proceed moist adiabatically up to 600 hPa. Subtract the 600-hPa dry bulb temperature from this value 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. (Note: Multiply this result by 1.15 to convert to mph, by 1.85 for kph, or by 0.51 for m/s)
Estimate the direction of the mean wind in the layer between 10,000 ft (3 km) and 14,000 ft (4.3 km) AGL. This will be the forecast wind direction of the computed gust.