Maximum wind velocity of convective wind gusts

The method of Ivens (1987) is used by the forecasters at KNMI to predict the
maximum wind velocity associated with heavy showers or thunderstorms. The
method of Ivens is based on two multiple regression equations that were
derived using about 120 summertime cases (April to September) between 1980 and 1983.
The upper-air data were derived from the soundings at De Bilt, and
observations of
thunder by synop stations were used as an indicator of the presence of
convection.
The regression equations for the maximum wind velocity (w- if T
_{x}- θ_{w850}< 9°C- w
_{max}= 7.66 + 0.653⋅(θ_{w850}- θ_{w500}) + 0.976⋅U_{850}

- w
- if T
_{x}- θ_{w850}≥ 9° C - w
_{max}= 8.17 + 0.473⋅(θ_{w850}- θ_{w500}) + (0.174⋅U_{850}+ 0.057⋅U_{250})⋅√(T_{x}- θ_{w850})

where

- T
_{x}is the maximum day-time temperature at 2 m in K - θ
_{wxxx}the potential wet-bulb temperature at xxx hPa in K - U
_{xxx}the wind velocity at xxx hPa in m/s.