Mountain Wave and Downslope Wind Events in the San Gabriel Valley of Southern California

Damaging wind events across the San Gabriel Valley and adjacent foothills associated with mountain waves and downslope winds that are produced by strong north to northeast flow over the San Gabriel Mountains can be difficult to predict. This is largely due to the inability of course resolution models to fully resolve the details of these events, along with their relative infrequency of occurrence. Although these events are rare, accurately forecasting them is critical because they can have a significant impact on densely populated communities, as was seen during an extreme event that occurred during the early morning hours on 1 December 2011.

The purpose of this presentation is to raise awareness of the impacts that mountain wave and downslope winds can have on the foothill and valley communities adjacent to the San Gabriel Mountains, as well as to show the synoptic scale conditions that tend to be associated with these events. This will be accomplished by examining the extreme event of 1 December 2011 in detail, then presenting a 35 year climatology of damaging wind events in the foothill and valley communities adjacent to the San Gabriel Mountains. The synoptic scale conditions of the 1 December 2011 event will also be compared to several events from the climatology.