Topographic and synoptic influences on cold season California severe weather: regional patterns in convective storms

Recent studies of tornado outbreaks in southern California by Hales, central California by Staudenmaier and Cunningham, and northern California by Braun and Monteverdi, have shown the importance of local topography in producing low-level convergence and favorable wind shear. The present study compares the above mentioned severe weather events, along with composites based on 25-years of California severe weather (1974-1999) by the authors, for regional differences and similarities in storm environments. The climatology of severe convective storms also reveals geographic preferences, which hinge on combinations of topographic and synoptic influences. Surface and upper air synoptic patterns indicate weaker updrafts and generally smaller sized storms compared to their Great Plains counterparts. Storm development often occurs in the cold sector, behind the cold front with lower warm air advection and low-level moisture than those east of the Rockies. However, strong winter cyclogenesis, powerful upper level jet streams, and vertical wind shears comparable to eastern values, can lead to local or widespread severe convective activity.