Early Wind Forecasting Results From The 1.5 km WRF-ARW In Extreme Southwestern California

Strong winds are a common occurrence in southern California. The most well-known are the Santa Ana winds (Jones et al., 2010). These are the generally hot, dry winds that blow from the desert to the sea. Lesser known are the onshore flow wind events (Small, 2006). During these events in southern California, the wind blows from a south through northwest direction, and can produce downslope winds as strong as a Santa Ana Wind event. Wind gusts in excess of 45 m/s (approximately 100 mph) have been observed with both types of events. Similar to Santa Ana Winds, we have had disruptions in air traffic due to strong mountain wave activity in onshore flow. As an example, on 26 March 2014 three jets were diverted from Palm Springs (KPSP) airport to alternate airports due to wind shear and mountain wave rotor activity. Such winds can also cause erratic wind shifts and can be especially hazardous during firefighting operations.

Recently, NWS San Diego has developed the capability to run a 1.5 km nest inside of our 3.7 km local WRF-ARW. In this paper we will explore some recent wind cases using the 1.5 km WRF. It has shown promise for analyzing and predicting the strength, location, onset, and cessation of surfacing mountain waves as well as timing of the sea breeze front. It is hoped that the output from the WRF model run locally at WFO San Diego will demonstrate the usefulness of a locally run non-hydrostatic model for forecasting windstorms.