Northwest California Severe Convection Episode of August 7, 2006: A Weather Event Simulator (WES) Case

摘要

Thunderstorms are infrequent across northwest California. The 30-year thunderstorm average yields only five such days annually at Eureka and 10 days per year at Red Bluff (Conway and Liston 1990). Although a somewhat higher incidence of convection and associated thunderstorm development could reasonably be expected over the intervening higher terrain, severe thunderstorm development is indeed very rare. Prior to this event, the last severe thunderstorm warning (suspected or confirmed winds of at least 50 kt and/or hail of or larger) issued by the National Weather Service office in Eureka was over 25 months earlier. Low to mid-layer instability accompanied by upper-level diffluence is a major contributor to thunderstorm outbreaks in northwest California, notwithstanding sometimes limited moisture availability. Areas in close proximity to the coast experience the vast majority of convective days during the winter and spring months, while inland areas show little seasonal preference for such activity.