Abstract:Based on the observed data and output data from MM5, the causes for the blizzard process in Hebei Province form November 10 to 11 in 2009 are analyzed. The results show that a cold front system influences Hebei Province for a long time and brings about positive and contrary bi directional secondary circulations with strong upward flows and convergence at the middle levels coupled with positive vorticity column, which are the main dynamic factors for snowstorm. On the other hand the results show that the conditional symmetric instability and convective instability are formed in the blizzard area due to the stronger temperature gradient and wind vertical shear. Moreover, plentiful water vapor is transported to Hebei through the southwest warm and wet airflows, which change into snow and ice by deposition and freezing when being carried to the higher cold levels. The northeast dry and cold airflows acting as a cold wedge of backflow snowfall are accumulated and lifted in the lower level because of the eastward bell mouthed topography. It favors development of severe convective weather when the two kinds of upward flows caused by topography and front surface secondary circulation are superimposed.