Unseasonably warm temperatures continue today with near record highs. Gusty north winds with downed trees and tree branches, localized power outages, and elevated fire weather concerns over the weekend. Much cooler with shower chances early next week.
Discussion
Satellite imagery shows the ridge shifting east as the large trough over the eastern Pacific approaches. Other than a few high clouds, skies remain clear ahead of the trough. Surface pressure gradients continue to relax and winds are considerably lighter across the northern Sierra and foothills early this morning (Jarbo Gap gusting to only 14 mph compared to around 40 mph 24 hours ago).
Current temperatures are very mild and range from the mid 50s to the lower 70s across the Central Valley, as much as 10-15 degrees milder at some of the warmer spots compared to this time yesterday. While the ridge will be shifting east today, synoptic cooling associated with the trough will mainly be confined to the northern half of the forecast area.
Temperatures further south will remain close to Thursday’s readings, and highs will be close to records across the Sacramento region and northern San Joaquin Valley.
Current records for today:
Redding/Redding Airport…..93 in 1989
Red Bluff……………….96 in 1989
Downtown Sacramento………91 in 1989
Sacramento Exec………….90 in 1989
Stockton………………..90 in 1989
Modesto…………………92 in 1989
The trough moves in later this afternoon and will initiate a brief period of gusty onshore flow. The onshore flow won’t bring much cooling due to a lack of marine layer along the coast. Mid and high clouds will increase this afternoon as the upper level front moves in.
Forecast soundings indicate some elevated instability late this afternoon into this evening, but moisture appears too meager and high-based to support deep moist convection, though virga may develop from the mid-level clouds.
Ensemble guidance remains in decent agreement indicating a prolonged period of gusty northerly winds for NorCal over the weekend as the trough moves east. Some of the broader resolution ensemble output indicates wind gusts may not be quite as strong as indicated yesterday, but the latest HREF shows potential for 45-55 mph gusts across portions of the Sacramento Valley and latest SLP forecasts indicate the MFR-SAC gradient tightening to around 14-16 mbs later Saturday.
So we’re still looking at a decent north wind event resulting in difficult driving conditions and potential for tree damage and local power outages.
The winds will also lead to elevated fire weather conditions, especially where seasonal grasses have already cured. Temperatures will also be significantly cooler over the weekend.
Another deeper trough is forecast to move into the region on Monday bringing a further drop in temperatures along with a chance of showers. The current trajectory of the system isn’t overly favorable for much precipitation in the valley, but widespread showers will be likely over the northern Sierra and some accumulating snow will be possible. Stay tuned.
Extended Discussion (Tuesday through Friday)
Confidence remains high in below normal temperatures and unsettled weather Tuesday through Friday, a big change from the heat of this week. Lows could drop into the upper 30s Tuesday and Wednesday morning for the Valley.
Some lingering light precipitation is possible over Shasta County and the Sierra crest Tuesday, but most of the area should see dry weather as the trough exits to the east. Ensembles show a reinforcing shortwave from western Canada arriving at some point Wednesday to Wednesday night, but timing and intensity of precipitation remains uncertain.
Confidence is a little higher for some showers on Thursday, but cluster variation still shows a lot of uncertainty for rainfall and snow amounts.