December 3, 2017 – Dry weather Monday through the week with breezy north winds Monday and cold morning lows.
A weak frontal band dropping southeastward over the northern Sierra this morning is currently dropping snow down to about the 5000 foot elevation. About an inch or two of snow has fallen so far and Caltrans sites are reporting chain controls on interstate 80 above 5000 feet. Snow levels will continue to fall behind the frontal band this morning, possibly down to the 3000 to 4000 foot level, but precipitation amounts will be waning by mid morning. Expect about 1 or 2 more inches of additional snowfall will be possible before the front moves through and precipitation ends. Precipitation has mainly ended in the valley this morning where only a couple of hundredths of an inch of rainfall fell. Some fog has formed in the central valley this morning but lingering cloud cover will hopefully keep it from becoming dense. By this afternoon, only a few lingering showers are expected over the Sierra crest with clearing skies elsewhere.
Behind the front tonight into Monday a northerly surface gradient will increase as upper flow becomes northerly. This will produce breezy to locally windy conditions most locations on Monday. At this time, wind speed forecasts in the valley remain a little under advisory speeds but surface gradients and upper support for north winds look good so winds could come in higher than forecast.
Cold air advecting into the region behind the front will lead to colder nighttime temperatures next week but daytime highs will warm as the airmass warms up under a building ridge. The coldest mornings look like they will be on Tuesday and Wednesday under lighter wind conditions and some locations in the valley could drop to around freezing. Otherwise a dry weather pattern with slightly above normal daytime temperatures will continue through mid week under anomalously strong high pressure.
Extended discussion (Thursday through Sunday)
Very little change to the extended forecast as a fairly strong ridge of high pressure will dominate most of the time. Ridge looks to be strongest in the extended periods from Thursday to Saturday and does break down slightly Sunday. End result is mild temperatures and cool nights through Sunday.