November 18, 2021 – Areas of morning valley fog, otherwise shower chances return later today and tonight and persist through Friday. Dry weather returns over the weekend with breezy north to east winds.
Discussion
Lots of high cloudiness ahead of the approaching weak system is spreading over NorCal early this morning as the ridge nudges eastward. Despite these clouds, areas of fog have redeveloped in the Central Valley with a few spots reporting visibility as low as 1/4 mile. Surface pressure gradients have weakened considerably since Wednesday and winds are generally light across the area.
Despite the high clouds, fog and low clouds will become a little more extensive through the valley south of Red Bluff early this morning, then is likely to mix out by late morning to early afternoon.
Weak systems moves through late today through Friday – first the weak southern stream system tonight followed by a short-wave dropping down from the northwest on Friday. QPF will be very light, less than half an inch in the mountains with only a few hundredths of an inch expected through most of the valley. The higher northern Sierra passes may see a dusting of snow on Friday, but impacts to travel will likely be minimal.
Dry pattern returns over the weekend with breezy northerly flow, especially Saturday as another short-wave “inside slider” drops down into the Great Basin over the building ridge. The north wind will limit the extent of late night and morning valley fog. High temperatures will return to a little above average with overnight lows close to normal.
Extended Discussion (Monday through Thursday)
Ensemble guidance and clusters favor troughing across the western US next week; however, there is much disagreement with the strength and placement of this feature.
For now, guidance keeps any early week precipitation to our north and have continued with the dry NBM forecast during this time. Near seasonable highs and lows are expected.