November 9, 2020 – Dry weather and below average temperatures continue through mid- week, with freezing Valley temperatures expected Monday and Tuesday mornings. Breezy north to east winds continue into Monday morning with lowering humidity. The chance for rain and snow returns late in the week and into the weekend.
Upper level low over the UT/AZ border forecast to move across the Great Basin today and into/across the Plains States on Tue. This will bring and end to the precip chances in Norcal, especially on the W side of the Sierra Crest. The Ewd movement of the upper low will allow the Nly and Ely pressure gradients to relax and the winds to decrease this afternoon, so it won’t feel as chilly today, although max temps will run some 4-10 degrees below normal in the Valley and double digits below normal in the mountains.
Clear skies and light winds tonight will allow for strong radiational cooling in the Valley with min temps nearing or dropping below freezing at many locations.
In the far Nrn portion of our CWA, an approaching short wave but weakening surface front is forecast to spread some cloud cover across the Nrn zones where we expect clouds and a warming air mass to moderate the min temps in the Burney Basin/Wrn Plumas Co mountain basins. However, that area will cool again Wed morning due to CAA behind the front and short wave.
Although NW flow aloft will moderate, below normal temps will continue into Thu with a chance of precip late Thu into Fri.
Model differences result in lower than normal confidence, but the GFS/ECMWF ensemble Prob of IVT plumes illustrate relatively “weak” TPW plumes in the mid latitudes nearing the W coast beginning day 4 (the 12th) and into the 13th and 14th which will impact Norcal.
Extended discussion (Friday through Monday)
Model differences with timing and depth of short waves puts some uncertainty in the extended forecast period. Main theme is periods of wet weather look possible although QPF amounts are in question.
Periods of mountain snow with some accumulation is also possible. Specifics will hopefully become more clear with future model runs.