Precipitation expected Sunday with moderate mountain travel impacts and a few light Valley showers. Mountain snow and very light Valley showers today. Strong northerly winds today into Monday. There is the potential for freezing and sub-freezing overnight low temperatures next week.
Discussion
Latest satellite imagery shows sunny skies across interior NorCal this afternoon. Valley highs this afternoon will reach into the upper 50s. Increasing cloud cover is expected tonight as a system approaches from the north, with overnight temperatures slightly milder than this morning.
A cold system with limited moisture from western Canada will drop southward into the area on Sunday morning, bringing with it light rain chances, mountain snow, and another round of breezy north winds.
Rain amounts in the Valley will be very limited with little to no accumulation. Some mountain snow accumulations remain likely. There is a 25-50% chance of 4+ inches at pass level, and 10-25% chance of 6+ inches.
Snow levels will initially start off around 2500-3500 ft on Sunday, then lower in the late afternoon and evening hours, falling to 1500-2000 ft (locally lower).
North to east winds will increase in this system’s wake Sunday afternoon and into Monday with a strong surface pressure gradient developing. Wind gusts in the 40 to 50 mph range are possible along the west side of the Sacramento Valley.
Even higher gusts will be possible for portions of the foothills, with gusts to 60 mph possible over exposed ridgetops, peaks, and gaps. NBM generally shows probabilities of 75-100% for wind gusts greater than 40 mph along the west side of the Sacramento Valley and the Sierra.
A Wind Advisory remains in effect from 1 pm Sunday to 1 pm Monday for the Sacramento Valley, Delta, northeast foothills, northern Coastal Range, and the Sierra Cascade Range.
A cold airmass filters in behind the system, with overnight temperatures at or below freezing early to mid next week. The ECMWF EFI also highlights the potential for cold overnight temperatures.
Even colder overnight lows will be possible Tuesday morning, with Valley lows around freezing down into the upper 20s. The probability of hitting 28 deg F ranges from 20-70 percent.
Best potential for hard freeze conditions will be across the northern San Joaquin Valley. High clouds spreading into the area still bring some uncertainty in how cold it will get at this point, though.
Extended Discussion (Wednesday through Saturday)
Cold morning low temperatures will continue on Wednesday and linger into Thursday, however temperatures will become more mild later in the week.
Ensemble guidance suggests a brief period of ridging midweek before another shortwave trough moves through later in the week. There is still some uncertainty in the cluster analysis, but light precipitation chances look to return with this trough Thursday into Friday.
At this point, precipitation amounts do not look impactful but will continue to monitor as we get closer. The National Blend of Models (NBM) currently has about 20 to 40 percent probability of an inch of mountain snow or greater at pass level and a 30 to 55 percent probability of a tenth of an inch of rain or greater in the Valley and foothills over 48 hours ending early Saturday morning.