Cooling trend this week. Smoke from area wildfires will persist over portions of interior NorCal, mainly foothill and mountain locations. Widespread shower chances return late Saturday into early next week.
Discussion
Flat zonal upper level pattern will prevail over Norcal today into Friday, as upper level low takes shape over British Columbia. Ensembles and clusters drop this low southward into the Pac NW Saturday and just off the Northern California coast, west of Eureka Sunday. This will bring much cooler temperatures Friday and especially Saturday, along with precipitation chance Saturday night into Sunday. Valley high temperatures today and Friday will be generally in the 80’s, cooling into the 70’s Saturday and 60’s and 70’s Sunday.
Rainfall amounts Saturday night and Sunday will generally be from 0.10 to 0.50 inches heaviest northern Sacramento Valley and Coast Range. A period of gusty ridge top winds are possible Saturday afternoon with southwest gusts from 30 to 35 mph, although increasing relative humidity values will help to mitigate fire weather concerns.
Extended Discussion (Monday through Thursday)
Ensemble and cluster guidance indicates the trough will continue deepening with a closed low spinning off of the Central California coast Monday. This is expected to bring widespread showers into Northern California early next week.
Cluster analysis indicates there is still uncertainty in exact timing, depth, and strength of the trough, but latest WPC Qpf guidance has increased precipitation amounts and overall confidence in a significant early season precipitation event is increasing. Light snow showers of less than an inch are possible at higher elevations above 7500-8500 feet Saturday night and Sunday night. Keep an eye out for updates on this system!