January 11, 2021 – Areas of dense night and morning fog much of the week. Light precipitation possible north of I-80 Tuesday and Wednesday. Above normal temperatures after mid-week with near record highs.
Discussion
High clouds moving through the upper ridge over NorCal limiting overall fog development so far despite slightly higher RH’s over most of the valley, but clouds will thin during the next few hours allowing more extensive dense fog to form by sunrise (especially from the around the Sacramento area southward into the San Joaquin Valley). DFA will remain in effect until late morning.
Mostly sunny skies expected across most of the area today as the ridge moves east. Temperatures will be a little warmer than Sunday once the fog and low clouds breakout by early afternoon with much of the Central Valley expected to see highs in the upper 50s and lower 60s.
Ridge flattens Tuesday and Wednesday as upper trough moves through the PacNW. NorCal will be on the periphery of a wide swath of deep moisture moving onshore to our north. Warm-advection increases across the far north end of the forecast area late tonight and persists through Wednesday allowing for a long period of light precipitation across the northern mountains where 1 to 2 inches of rainfall will be possible north of Redding by late Wednesday. Snow levels will rise to above 7k ft, so winter travel impacts not expected.
Sunshine and warmer temperatures return Thursday as amplifying ridge moves over NorCal. Highs Thursday will approach record levels for the date and will be around 10-15 degrees above average over most of the area.
Extended discussion (Friday through Monday)
Weak system moves through strong upper ridge late Friday, but forecast remains dry attm. Otherwise upper ridge remains the dominant synoptic feature with models showing it strengthen off the West Coast early next week. As a result, dry weather will continue with high temperatures upwards of 10 to 15 degrees above normal.