WILDFIRE-FAVORABLE OFFSHORE WIND EVENTS IN CALIFORNIA: GLOBAL-SCALE CLIMATE TELECONNECTIONS TO EXTREME WEATHER AND POTENTIAL SUBSEASONAL TO SEASONAL PREDICTABILITY

Abstract

Wildfire-favorable offshore wind events (OWEs) in California, such as Santa Ana (SA) and Diablo wind events, are extreme weather events that can contribute to severe societal impacts. We analyzed the large-scale weather and climate conditions associated with OWEs in California during November 1979–2018. We focused on statistical and dynamical analyses of the associated global subseasonal to seasonal (S2S) atmospheric and oceanic anomalies. We found that OWEs in California tend to be part of anomalous planetary wave trains that span all or most of the northern extratropics and that they appear to be initiated by sea surface temperature anomalies (SSTAs) and tropospheric convection anomalies in the tropical Indian Ocean and western-central tropical Pacific region. Multiple lines of evidence suggest that the onset of the tropical anomalies tends to lead the occurrence of November OWEs in California by 10–30 days or more. An empirical test shows that: (a) using the MJO as a predictor of California OWEs at subseasonal lead times produces skillful forecasts compared to random forecasts; and (b) the impacts of MJO are modulated by low-frequency climate modes (e.g., ENLN and ENLN Modoki). We also analyzed OWEs in October and December 1979–2018 and found broadly similar results. Our results strongly suggest that skillful S2S predictions of California OWEs may be possible by accounting for tropical atmosphere-ocean variations and tropical-extratropical teleconnection dynamics.