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In this paper, the Extreme Forecast Index (EFI) related to short-time heavy precipitation, thunderstorm gale and hail in Zhejiang is calculated using ECWMF ensemble prediction data and Zhejiang automatic station observation data from 2016 to 2021. The characteristics of EFI are analyzed, and the forecast model is built. Results show that severe convective weather is closely related to the EFI of physical quantities. When short-time heavy precipitation occurs, the physical quantities with larger EFI are convective effective potential energy, whole layer precipitable water, temperature difference and potential temperature difference between 850 hPa and 500 hPa. While the EFI of vertical wind shear is negative, indicating that the smaller vertical wind shear is more conducive to the occurrence of extreme precipitation. When thunderstorms and hailstorms occur, the physical quantities with a larger EFI index are convective effective potential energy, temperature difference and potential temperature difference between 850 hPa and 500 hPa, and temperature dew point difference of 850 hPa. EFI of dew point temperature of 700 hPa is negative, related to the favourable stratification condition of the dry and cold upper layer with the warm and wet lower layer. By using the multi-classification method of the Support Vector Machine, the EFI of the physical quantities related to the strong convective weather are used as the characteristic value to carry out training. The prediction model is effective for nonlocal severe convective weather, and the misjudgment rate of short-term heavy precipitation is obviously lower than that of thunderstorm gale.