Scattered light rain showers are expected across interior Northern California today. Critical fire weather conditions are then expected Thursday night through Saturday evening from gusty winds and low humidities. Red Flag Warning from 11 PM Thursday to 5 PM Saturday. Seasonal temperatures are then forecast for early next week.
Discussion
While 2am Valley temperatures are currently up to 10 degrees warmer than they were 24 hours ago, that should change later today as the expected shortwave trough moves through NorCal.
In addition to cooler daytime highs, this shortwave will bring some light precipitation to the area; generally less than a tenth of an inch in the Valley, and around a quarter of an inch or less at higher elevations. Additionally, there is around a 20% probability for isolated thunderstorms in the mountains this morning, primarily north of I-80.
Thursday, north to east winds begin to pick up and minimum daytime humidities begin to drop as an “Inside Slider” pattern begins to take hold with a larger trough beginning it’s path down from the north, over California, and into the Great Basin. Elevated to critical fire weather conditions are expected Thursday evening through early on Saturday evening, with wind speeds peaking and relative humidities bottoming out sometime on Friday.
The most critical conditions will occur along the western edge of the Sacramento Valley (up to the I-5 corridor) and the Delta, though most of the overall Valley, Delta, and northeast foothills will see fire weather concerns. The NBM currently has a 40 to 85% chance of wind gusts that are 40 mph or higher in the specific areas mentioned above, with a broader chance of 50 to 95% of gusts that are 30 mph or higher across the Valley and northeast foothills.
Minimum relative humidities will generally be between the single digits and 20% with poor to moderate overnight recoveries. A Red Flag Warning is currently out from 11pm Thursday through 5pm Saturday due to these conditions. There is also a Wind Advisory in place in the Delta and along the western side of the northern San Joaquin Valley.
Extended Discussion (Sunday through Wednesday)
On Sunday, the upper low causing elevated fire weather concerns fills and moves off to the east, allowing some ridging to build into the area. This will result in dry conditions and seasonal temperatures in the 70s across the area. These conditions look to persist through Wednesday of next week. While yesterday, it looked like there would be potential for some precipitation early next week, current ensemble solutions look to have the low bringing those chances staying off the coast a while longer. The 90th percentile of the NBM remains unconvinced but for now, precipitation chances across interior NorCal remain limited to the meager rainfall we’re expecting today.