Weak system enters the area today bring Valley rain and moderate mountain snow through early tomorrow morning. Scattered mountain snow showers continue through Friday, then quieter weather arrives this weekend through into next week.

Discussion

Quiet weather prevails across NorCal this Wednesday morning. Quiet and dry weather will not be around for long, as our next weather system moves into the area later this morning from the Pacific Northwest.

Rain impacts

Rainfall totals through Thursday morning have trended slightly up this morning, as Valley totals are now around 0.25″ inches to 0.75″ inches, with higher totals south of I-80. As a result, NBM probabilities have around a 40-60% of exceeding 0.50″ inches from Sacramento southward into the northern San Joaquin Valley. Higher probabilities of 60-80% exist in the Foothills and the northern Sierra for exceeding 0.50″ inches of rainfall through Thursday morning.

Snow impacts

Snowfall totals have trended upwards this morning as well, as the system moves in orographic lift will enhance snowfall rates in the Sierra. Snow levels will begin around 4000 feet and fall to around 3000 feet early Thursday morning. The heaviest snowfall is expected late morning into the afternoon time frame today, before gradually diminishing Thursday morning. With the uptick in snowfall totals, NBM probabilities for 8 inches of snow or more are around 50-70% along I-80/HWY 50 at elevations greater than 5000 feet. Little to no snowfall is anticipated along I-5 in Shasta County at the higher elevations.

Periods of moderate snow will impact the Sierra and southern Cascades Wednesday-Thursday AM, forecast snow totals have trended up. Expect 6-12 inches of snow above 4500 feet. Be prepared for travel delays, snow-covered roads, and possible chain controls.

A Winter Weather Advisory went into effect at 4AM PST this morning through 4AM PST Thursday morning for elevations greater than 4500 feet in the Sierra. Hazardous driving conditions could impact the morning or evening commute.

The bulk of the heaviest winter precipitation and Valley rainfall will be out of the area Thursday afternoon, as the system begins to move off to the southeast. NorCal will still be under the influence of upper-level troughing Thursday and Friday, so isolated mountain snow showers and Valley rain showers cannot be ruled out, although impacts will be minimal.

On Saturday, the upper-level low finally moves off into the Four Corners region, and upper-level ridging will begin to develop over NorCal. High temperatures on Saturday will begin to make their way into the upper 50s and low 60s across the Valley, as the developing ridge begins to strengthen and dominates the pattern as we move into next week.

Extended Discussion (Sunday through Wednesday)

EPAC upper ridging progged to be dominant synoptic feature through the extended forecast period. Several short waves move through the ridge at times but waves look too weak and trajectories far enough north to keep the forecast dry. High temperatures Sunday into Wednesday forecast to be near to slightly above average.

Precipitation Probability Hazard

There is some potential for a storm system by President's Day Weekend. Stay tuned for updates.