High clouds continue to stream into far northern California from the west while clear skies cover the remainder of interior NorCal. Current temperatures range from the mid 30s in the colder mountain valleys to the mid 50s to mid 60s across the Central Valley.
Slight cooling is expected across the region today as high pressure weakens slightly ahead of the approaching trough and surface pressure gradients trend toward a little more onshore. A noticeable cooling trend will start Tuesday and continue much of the week as trough deepens.
Temperatures will cool to below- average and locally breezy/windy conditions are expected. Minimum temperatures will be the coolest so far this season with sub- freezing readings possible in the mountain valleys.
The Central Valley will see chilly nights as well with some areas likely to dip into the 40s. While the system is expected to be mainly dry for interior NorCal, the latest operational model runs are indicating the potential for a few showers across the far northern portion of the state late Wednesday afternoon and evening as a short-wave brushes the area.
Extended Discussion (Friday through Monday)
Longwave troughing will persist across the West Coast through at least this Friday. The GFS and ECMWF disagree with how quickly to eject this trough eastward this weekend, with the ECMWF being much more progressive with the 00z runs than the GFS. A blend of the two solutions yields a temperature forecast at or slightly below normal through the extended period. Dry weather is likely to continue across the region in this timeframe, as precipitation remains well to our north.