January 7, 2021 – Morning fog and dry weather are expected today. A wetter system Thursday night through Friday could bring some rain and several inches of mountain snow. Dry and mild weather is forecast for the weekend with morning Valley fog.
Discussion
A shortwave ridge developed as the quick moving shortwave that brought some precipitation yesterday exited to the east. Dry weather returned overnight with clearing skies, light winds and wet ground bringing fog spreading into the Valley by late evening. A Dense Fog Advisory was issued for the central Sacramento Valley, southern Sacramento Valley, Carquinez Strait and Delta and northern San Joaquin Valley Counties through 11 am PST Thursday. Northerly winds have developed after midnight along the western side of the Valley, though, which are diminishing the denser fog in that area. Also, some high clouds from another shortwave trough off the coast are spreading in. For now will scale back the area of the Dense Fog Advisory (through 11 am) to the eastern side of the Valley, which is more sheltered from the northerly winds. This area includes western Placer County, eastern Sacramento County, eastern San Joaquin County and eastern Stanislaus County and the lower levels of the adjacent Motherlode.
After the morning fog clears, expect some high and mid level clouds over the area today. Temperatures will be about the same as yesterday except for the northern Sacramento Valley, where it should be about 5 to 10 degrees warmer. This means mid 50s to around 60 for the Valley, Delta and foothills.
Late this evening, another quick-moving system will spread inland and bring precipitation to much of the area through Friday. Precipitation amounts should be generally fairly light for this second system, with amounts at/below 0.10 inches from Sacramento and points south, and about 0.10 to 0.25 inches for the central and northern Sacramento Valley.
Mountain and foothill locations north of I-80) would be favored to receive more, generally between 0.25 and 0.50 inches, while further south would see around 0.10 or less.) The northern San Joaquin Valley may see little or nothing in terms of rainfall. Above 6000 feet in the northern Sierra 2 to 4 inches of snow are possible. The Lassen Park and western Plumas County higher mountains could see 3 to 6 inches of snow, as well as the higher peaks in northern Shasta County.
Dry conditions return to the region for the weekend with morning fog likely to return as an upper level ridge begins to set up residence over the West Coast. Partly cloudy skies with above normal afternoon high temperatures are forecast.
Extended discussion (Monday through Thursday)
Longwave ridging will result in mainly dry and mild weather for the region next week. The far north end of the forecast area may see some light precipitation at times as the tail end of weak systems pass thru the ridge. Pattern favors late night and morning valley fog.