Abstract: Based on the conventionally observational data and the NCEP/NCAR reanalysis data, a hail weather process on June 6, 2009 in the northern Hubei province was analyzed, and the lifting trigger, water vapor and unstable conditions before this process were diagnosed. The results indicated that the surface meso-scale convergence line is the uplifting conditions of this hail process, which leads to the severe convective weather. A dry layer in the middle and low level effectively inhibits the development of convection in the boundary layer and creates favorable conditions for the accumulation of unstable energy. The formation of surface dry line increases potential atmospheric baroclinicity and promotes the development of the secondary circulation, thus atmospheric instability is increased. The analysis based on Doppler weather radar and lightning location data shows that reflectivity intensity of radar echo, echo top heights and vertical integrated liquid water (VIL) increase rapidly, and it is indicative to hail weather. Moreover, the peak values of lightning frequency during 10 min are important to hail warning if they appear more than 20 times ahead of hail occurrence.

Key words: Hail, Meso-scale convergence line, Dry lay, Dry line, Diagnostic analysis