Two rounds of rain and heavy mountain snow through Sunday morning

March 23, 2018 – After a brief break, wet weather will return by tonight and continue into the weekend. Snow levels will lower with significant snowfall accumulation expected into the weekend.

Discussion

What a difference 24 hours makes. The mild airmass with deep moisture has been shunted to the south and east by yesterday afternoon’s cold front replaced with a colder and drier airmass. Current temperatures are running 10-20 degrees cooler compared to 24 hours ago, and DP’s are running 15-30 degrees lower.

The break in precipitation overnight won’t last too much longer. Showers will develop across the northern portion of the forecast area by midday as the next system drops down from the Gulf of Alaska. The next cold front will drop south tonight bringing showers to the Sacramento region and renewed snowfall to the northern Sierra Nevada. Ahead of it, gusty southerly winds will increase across the region today.

That will be followed by a second even colder system which will move southward Saturday afternoon and night. A few thunderstorms will be possible Saturday afternoon across the northern Sacramento Valley.

Snow levels will lower to around 1500 feet in Shasta County and 3000-4000 feet in the northern Sierra Nevada by Saturday. With the cold and convective nature of these systems, snow ratios will be much higher than the past several days. Heavy snow is likely with 1-3 feet of fresh accumulation across the mountains, and a winter storm warning has been posted with significant travel impacts expected.

Diminishing showers are expected by Sunday night as the trough shifts into the interior West and ridging from the eastern Pacific begins to edge onto the West Coast. Gusty north winds and milder temperatures are expected Monday.

Extended discussion (Tuesday through Friday)

Upper level high pressure building over the eastern Pacific and west coast will bring fair skies, warmer than normal temperatures and light northerly breezes by the start of the extended period next Tuesday.

Temperatures will continue to warm Wednesday and Thursday as the upper ridge centers over the west coast and the airmass over NorCal warms.

By Thursday afternoon, daytime highs will warm to 10 or more degrees above normal some areas. The upper ridge is forecast to weaken slightly next Friday as a weak system passes to the north. This will bring a slight drop in daytime temperatures but highs will continue to run well above normal.