A few showers or thunderstorms will persist over the Sierra today, otherwise cool and dry weather will continue through the weekend. Breezy northerly winds in the Sacramento Valley will decrease by this afternoon. Pattern change will bring increasing rain chances early next week.
Red Flag Warning until 5 PM PDT this afternoon for Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-Northern Sacramento Valley to Southern Tehama County Line below 1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes portions of Shasta-Trinity and Butte Units-Southeast Edge Shasta-Trinity NF and Western Portions of Tehama-Glenn Unit-Southern Sacramento Valley in Yolo-Sacramento Far Western Placer, southern Sutter and Solano County below 1000 ft elevation.
Discussion
The deepening closed low is over eastern Oregon early this morning. The system has been responsible for a few showers and thunderstorms over the foothills and northern Sierra overnight as a cold front moves south, but precipitation amounts have been very light. Elsewhere, skies remain clear with cooler temperatures compared to 24 hours ago. Valley readings are in the upper 50s to around 70 currently.
Northerly surface gradient has tightened behind the front resulting in gusts of 25-35 mph across the northern Sacramento Valley and along its western edge. Humidity in this area has also lowered (remained low) and is generally in the 20-30 percent range currently resulting in critical fire weather conditions, and a Red Flag Warning remains in effect today.
The low will only drift a bit further south today, into southeast Oregon or north central Nevada, before moving east tonight and Friday. The northern Sierra will continue to see a chance for showers and a few thunderstorms today, but activity is expected to taper off quickly by this evening.
Improvement in air quality is expected this morning as the front moves through, but smoke may return late tonight and Friday especially for areas north of Sacramento.
Dry and mild weather is expected over the weekend with high temperatures around 5-10 degrees below average. Winds will be lighter and overnight lows will be on the cool side with upper 40s to mid 50s in the valley, and upper 20s to mid 30s in the mountain valleys. Clouds will begin to increase across the northern half of the forecast area later Sunday as the weather system for early next week approaches.
Extended Discussion (Monday through Thursday)
Pacific frontal system forecast to spread precipitation into NW portions of the CWA Monday afternoon into night, with some model differences on how fast the front progresses into the CWA.
Trend has been to slow the onset of precip. Models then spreads precip SE over the forecast area Monday night into Tuesday. Bulk of storm QPF looks to be from I-80 northward. WPC storm total QPF forecasts for the Central Valley are for less than a tenth around the Sacramento area to over an inch in Redding.
For the foothills and mountains north of I-80, storm totals are generally between a third and 1.5 inches.
Gusty winds will accompany the baroclinic zone as it moves through. Drier weather expected midweek as interior NorCal comes under the influence of upper level ridging. High temperatures trend up through the extended period but remain below normal. For the Central Valley, highs will be in 70s to lower 80s.