Two storm systems will impact NorCal next week

November 10, 2017 – Showers and light higher elevation snow today. Dry weather for Saturday into Sunday. Next storm system arrives Sunday evening into Monday with another round of rain and high elevation snow. Next system comes through around mid week.

Discussion

IR satellite imagery shows upper low off the Pacific Northwest coast has begun to shift inland. Models indicate that an upper trough will rotate through NorCal this afternoon bringing showers to much of the CWA except possibly for areas south of Stockton. Snow levels will come down slightly but precipitation amounts are not likely to be high enough to create significant travel issues. Stability progs do not indicate a high likelihood of thunderstorm activity this afternoon but an isolated thunderstorm may be possible. Should see daytime highs today similar to Thursday highs under similar airmass.

The upper trough shifts east of the forecast area tonight with high pressure aloft beginning to build in by morning. Clearing skies and surface moisture will bring the possibility of patchy morning valley fog especially southern Sacramento and northern San Joaquin valleys. Otherwise, Saturday looks dry under temporary high pressure ridge.

This ridge breaks down quickly as next Pacific frontal system pushes towards the west coast on Sunday. As early as Sunday morning, light overrunning precipitation could begin to fall over the northern zones. Snow levels will start out moderate then rise some by Sunday evening as warm advection continues.

Models push a Pacific cold front through NorCal on Monday bringing at least a chance of precipitation to the entire forecast area. Snow levels begin to fall by Monday night after frontal passage but by then most of the precipitation will be ending.

Extended discussion (Tuesday through Friday)

Next week the weather looks unsettled with below normal temperatures, coolest on Wednesday.

Tuesday is expected to be dry, a brief break from a series of storms as a shortwave trough exits to the east. With clearing skies and light winds, the day should start with cool temperatures. Afternoon highs are forecast to be below normal, reaching only the upper 50s to lower 60s in the Valley, Delta, and lower foothills.

The next system arrives Wednesday, with widespread precipitation by afternoon. There is some potential for a very wet system with low snow levels (latest GFS), but models continue to disagree on the strength and exact track of this system. Either way, this storm looks like it will bring some mountain travel issues Wednesday through early Thursday. Drier weather is expected for Friday, with the weekend uncertain.