October 15, 2018 – Red Flag Warning remains in effect until 11 pm. Critical fire weather conditions will continue through this evening across portions of interior northern California due to a combination of gusty wind, and low humidity. Winds will decrease slowly this afternoon and evening, but will remain breezy over the foothills and west slopes of the Northern Sierra Nevada into early Tuesday.
Discussion
Satellite imagery indicates the area of strongest subsidence is presently over NorCal on the backside of the upper trough digging southward through the Great Basin toward SoCal. Northeasterly surface pressure gradients topped out Sunday evening around 5 mbs RDD-SAC and 12.5 mbs RNO-SAC, and have tapered a bit since.
Currently still seeing quite a few wind gusts in the 30-40 mph range through the foothills, Coast Range and northern Sierra with a couple spots reporting gusts around 50 mph. Winds in the Sacramento Valley are mostly in the 15-30 mph range. The gusty winds will continue for several more hours before beginning to subside after sunrise. Lighter winds are expected by this afternoon.
Dry weather with mild days and cool nights will continue through the week. East winds will pick up again tonight in the northern Sierra as easterly gradients linger, but won’t be as strong. The combination of winds and low humidity has resulted in critical fire weather conditions. A Red Flag Warning remains in effect through this evening.
Lighter northerly flow will continue on Tuesday and fire weather conditions may continue to be an issue with little improvement in humidity levels. This will have to be closely monitored.
Extended Discussion (Friday through Monday)
Ridge of high pressure over the eastern Pacific is anticipated to shift onshore late this week, continuing the dry weather pattern across interior NorCal. Daytime temperatures will be 5-10 degrees above normal, with Valley highs in the 80s. Model guidance is suggesting the potential for unsettled weather early next week, as an upper trough approaches the West Coast. However, confidence is low this far out. Stay tuned.