- Above normal offshore wind events through January.
Weather and Fuels Discussion
October 4, 2020 - High pressure over the Great Basin and Desert Southwest was the dominant weather feature and it brought above normal temperatures to the region most of September. However, a couple of troughs moving inland to the north brought brief periods of near to a little below normal temperatures. Also, smoky skies moderated temperatures, especially across Central California. The high pressure was exceptionally strong from September 5th – September 6th, when some locations received their hottest days ever. Many valley locations received temperatures between 110 and 120 degrees on these two days. Overall, most locations received above normal temperatures for September (Fig 1). There was little or no rainfall across the entire region this month (Fig 2). Moisture from the remnants of Tropical Storm Karina brought scattered light showers with less than a quarter inch of rainfall to the Central and Eastern Sierra the night of September 17th through the afternoon of September 18th. Otherwise, only isolated thunderstorms occurred over the Creek Fire in the Central Sierra September 5th – September 6th. There was one weak Santa Ana wind event and it occurred on September 10th. There was little change to the drought situation across the region in September (Fig 3). Moderate drought to abnormally dry conditions continued across interior portions of Central California north of Kern County and across the deserts. Otherwise, there was no drought. The 1000 hour dead fuel moisture remained near or below the third percentile across much of the region and some areas across Southern California broke record low values (Fig 4). The 100 hour dead fuel moisture also was near or below the third percentile and broke record low levels across most of the region during the early and middle parts of the month (Fig 5 below). The live fuel moisture has dropped mainly to between 50% and 70%. However, a few old growth fuel moistures are running between 40% and 50%. These live fuel moisture values are a little below normal for this time of year (Fig 6 below).
South OPS Outlook
There has been little change in sea surface temperatures from the prior month. Sea surface temperatures remain well above normal over the Gulf of Alaska and across the West Coast, while sea surface temperatures remain well below normal over the Equatorial Pacific (Fig 7). Long term computer models are not expecting much change in sea surface temperatures for the next several months. This will most likely cause high pressure off the California Coast to be the dominant weather feature from October through January. This ridge of high pressure off the coast will bring above normal temperatures and below normal precipitation to the region. Also, offshore wind events are expected to be above normal as troughs are forced down into the Great Basin from the Pacific Northwest. Even though precipitation is expected to be well below normal and temperatures above normal into the winter months, the potential for large fire will most likely drop to near normal across Central California starting in November as temperatures cool. The large fire threat will most likely continue to be above normal across Southern California through December due to the expected above normal amount of Santa Ana wind events. However, enough rainfall will most likely occur across Southern California by January to lower the large fire threat to near normal.
