821 A Climatology of Warm Season Elevated Thunderstorm Events in Extreme Southwest California

Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Stephen J. Harrison, NWS, San Diego, CA

Warm season elevated thunderstorm events in extreme Southwest California are notoriously difficult to forecast. This is primarily because the mid or upper level forcing that initiates this type of thunderstorm is often subtle and the required amount of instability appears to vary significantly. The events can be high impact, as sometimes the dry sub-cloud layers and typically dry fuels in the warm season can result in numerous fire starts. These thunderstorms can impact the highly populated coastal areas not accustomed to lightning where beach goers and those attending outdoor events can be at a risk from cloud-to-ground lightning strikes. One example of this took place on July 27, 2014 when a person at Venice beach in Los Angeles County was killed by a lightning strike and several were injured. What enhances the danger for the coastal areas is the frequent presence of a marine cloud layer which can hide the cumulonimbus clouds and the visual threat for potential lightning. These events can result in hundreds of cloud to ground lightning strikes, severe hail, locally heavy rain and high wind gusts as well.

The intent of this study is to perform a climatology of instability and moisture parameters from the NKX (Miramar) upper air sounding RAOB for at least 20 warm season elevated moist convection events. The goal is to better understand the necessary ingredients and improve forecasting of these less common but higher impacting events in extreme Southwest California. The focus of the study will be on thunderstorms not rooted in the boundary layer and lightning which occurs outside of the diurnal peak heating and terrain driven moist convection. The results and applications of this study will provide forecasters with information and tools to enhance impact decision support to emergency managers and the general public in advance of these events.

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