Abstract:

Based on the meteorological observations from 169 meteorological stations and the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data with resolution of 1°×1° in the eastern region of Northwest China from 2008 to 2013,weather types of thunderstorm days were classified using calculated convective parameters,and the operational forecast of thunderstorm in 2013 was carried out according to parameter thresholds of different weather types.The results show that thunderstorm days mostly occur from May to September and account for 85.9% of the total thunderstorm days during this study period.There are four weather types of thunderstorm days,including the lower vortex type,the lower trough type,the northwesterly flow type,and the southwesterly flow type.The automatic identification method of the four weather types is investigated by introducing a weather type intense index,and it is examined to be able to identify different weather types correctly with fewer omitted samples.The physical diagnostic analysis by weather type identification indicates that the omitted samples decrease significantly.The threat score (TS) of back-substitution forecast on thunderstorm days in the eastern region of Northwest China from 2008 to 2012 is 54.1%,with four days of omitted samples,while TS of operational forecast on thunderstorm days in 2013 is 51.8%,with ten days of omission.TS in back-substitution forecast and operational forecast is both larger than climatic probabilities,which means the forecast performs good and can provide a reference to the study on a thunderstorm in the eastern region of Northwest China.

Key words: Thunderstorm, Weather type, Physical diagnostic analysis, Statistical forecast