November 20, 2019 – Unsettled pattern with breezy to windy conditions, cooler temperatures and showers over mainly the Sierra Nevada south of I-80. Milder weather returns for the weekend.
Satellite imagery shows the deepening closed low, presently south of the Bay Area, dropping southward just off the coast. Radar still showing a few showers in the Sacramento area in the deformation area to the north of the low. More extensive showers are occurring along and east of the northern Sierra crest.
Northerly surface pressure gradients have tightened considerably since Tuesday afternoon and the KMFR-KSAC gradient is now nearly 14 mbs. Northerly wind gusts have been ramping up and we`re now seeing some gusts of 35-45 mph over the northern and western portions of the Sacramento Valley, and locally in the foothills and northern Sierra Nevada.
The low will move south into SoCal today with shower chances becoming mainly confined to the northern Sierra south of Tahoe. Northerly winds will continue to increase into this afternoon when gusts are expected to peak as subsidence and upper level support max out. Gusts of 40-50 mph will be possible in the Sacramento Valley and surrounding terrain north of Sacramento.
Wrap-around showers may linger tonight along the northern Sierra crest, but winds will begin to decrease this evening and will be much lighter on Thursday. Varying amounts of cloudiness are expected into the start of the weekend with a little milder temperatures.
Extended discussion (Sunday through Wednesday)
Eastern Pacific ridging will bring mild and dry weather Sunday, with highs 5 to 10 degrees above normal, reaching the mid 60s to around 70 in the Valley and Delta. Winds are forecast to be northerly but light. Overnight lows in the light winds will be cool, dropping into the 30s and low 40s for the Valley, foothills, and Delta.
Model ensembles continue to suggest a shortwave tracking southward into the Great Basin. Any precipitation should remain north of the area. The main concern continues to be possible breezy northerly winds with low humidity Monday. This could bring enhanced fire weather danger if it occurs, but ensembles continue to show quite a bit of uncertainty.
Confidence is increasing some for a moister system on Tuesday and Wednesday. While not a very wet system, this could potentially be the first widespread precipitation event for the area seen in a while. This could also potentially bring some mountain snow on Wednesday, which is a major travel day before Thanksgiving. Confidence in the details is low this far out, though, but the system will be watched closely to see how it develops.
Temperatures trend downward next week, dropping to below normal by Wednesday. Valley highs may remain in the 50s.