Weak weather systems will bring a chance of light precipitation to mainly the northern mountains Tuesday and again later Thursday. These systems may be enough to disrupt the fog and low clouds covering the Central Valley. Warm and dry holiday weekend. Gradual warming trend mid-week into the weekend. Widespread Valley temperatures in the 60s this holiday weekend.
Discussion
IR difference imagery shows fog and low clouds moving north into the northern Sacramento Valley early this morning with visibilities of 1/4 mile or less currently at Oroville and Chico, while stratus is entrenched in the valley further to the south with visibilities currently around 2 to 5 miles. The fog and low clouds will once again be likely slow to clear much of the valley today as high clouds spread overhead with the upper ridge limiting overall mixing. Highs will likely be only in the 40s across the Central Valley, around 5-10 degrees below average. Current thinking is that dense fog will be less likely and less extensive Monday night as most of the valley likely won’t see much clearing from the stratus today. HREF guidance reflects this with lower probabilities of low visibility tonight.
The first of two weak systems will move through the ridge late tonight and Tuesday and may bring some light precipitation to mainly the northern mountains. The system may bring just enough mixing to disrupt the fog and low clouds across the valley as forecast soundings show potential for a little warming on Tuesday.
Ridge rebuilds Wednesday and Thursday, then another weak system brushes across the region later Thursday into early Friday with potential for very light QPF mainly across the far northern portion of the state.
Extended Discussion (Friday through Monday)
Strong ridging favored by the ensembles and clusters late this week through the weekend. The pattern will be favorable for more widespread fog and low clouds through the Central Valley and lower foothills over the weekend as a strong persistent inversion sets up.
Above the fog/stratus layer, very mild temperatures are expected with highs likely to be 10 degrees or more above average.
Signs are pointing toward a return to wet weather next week as the ridge shifts east allowing zonal flow across the Pacific to reach the West Coast, however clusters indicate some uncertainty on how quickly the pattern will evolve.