Dry and mild weather into early next week with chilly nights in the valleys.
Discussion
Clear skies across interior NorCal early this morning other than a few high clouds spilling over the West Coast ridge. A tight easterly surface pressure gradient is resulting in some locally gusty east winds along with very dry conditions in the northern Sierra Nevada. Current temperatures range from the teens to lower 20s in the mountain valleys, upper 20s to upper 30s in the Central Valley, and 40s to lower 60s across the foothill and mountain thermal belts.
Strong high pressure will continue the dry and mild weather pattern through the end of the week. Little overall temperature change expected through the end of the week with dry and mild weather continuing under a strong subsidence inversion. Highs will remain above average.
The ridge will weaken Friday as a short-wave trough brushes by to the north, but precipitation chances will remain to our north over the Pacific Northwest. This system will bring some cooling across the area but highs will remain above normal.
Chilly overnight temperatures will continue in the Central Valley beneath shallow nocturnal radiative inversions that develop each night with patchy frost likely.
Extended discussion (Sunday through Wednesday)
Upper ridge over the west coast will bring continued fair skies with daytime temperatures well above normal for mid December. Breezy north winds will continue Sunday but will be on the decrease as surface gradients begin to relax. By Monday afternoon, upper ridge axis centers over the west coast with light northerly gradients bringing only light or light north winds most areas. Little change is expected on Tuesday as the upper ridge moves slowly inland with daytime highs remaining on the order of 10 degrees above normal. Extended models show a weakening of the upper level west coast ridge by the middle of next week as a weak low drops into the Pacific northwest. Models differ on timing and strength but at this time it appears any precipitation will remain north of the forecast area. Daytime highs will remain above normal as well.