Cooler and more unsettled weather returns today and Tuesday as a cold weather system affects the region. Behind the system, freezing temperatures will be possible in the Central Valley each night during the mid and late part of the week.

Winter Weather Advisory from 4 PM this afternoon to 10 PM PST Tuesday for Motherlode-Northeast Foothills/Sacramento Valley and Western Plumas County/Lassen Park.

Winter Storm Warning from 4 PM this afternoon to 10 PM PST Tuesday for West Slope Northern Sierra Nevada.

Discussion

The upper trough is moving into NorCal with the initial strong vort dropping southeast across northeast California. Strong forcing with this feature is generating scattered showers across Sierra and Plumas Counties early this morning. Cold air continues to filter into the region with readings running around 5-10 degrees cooler compared to 24 hours ago across much of the area. After the recent stretch of mild weather, it will be a dramatic change toward cooler and more unsettled weather today and Tuesday.

The first batch of showers over the Sierra will taper off this morning as the vort slides southeast. Showers will then increase later this afternoon and overnight tonight as the main upper trough approaches, and will continue on Tuesday as the system closes off over western Nevada. Showers will taper from the north later on Tuesday as the trough shifts east.

Significant winter weather impacts are expected over the northern Sierra tonight and Tuesday where QPF and snow amounts are trending higher. 8-12 inches of snow will be possible above 4k ft, and 1-2 feet above 6k ft leading to travel disruptions.

An upgrade to a Winter Storm Warning has been issued. Lighter snow amounts will be possible in the foothills, and further north in the southern Cascade Range. A dusting of snow may occur down to around 1k ft in the foothills.

Behind the system, cold air will settle into NorCal with freezing temperatures likely across the Central Valley during the middle and later portion of the week, and a Freeze Watch has been posted. At this point, it appears the coldest morning will be on Thursday when lows may drop into the mid 20s across portions of the valley. Northerly breezes may help to moderate temperatures a bit along the western edge of the valley.

Extended Discussion (Friday through Monday)

Cool temperatures will be left in the wake of a trough digging through the region. Friday morning is looking to be another chilly start for interior Northern California. A Freeze Watch has been issued for the low minimum temperatures expected across the Valley by mid week that will continue in to Friday morning. Low temperatures could near daily record lows for the Sacramento metro area and northern San Joaquin Valley.

Ensemble guidance is in good agreement high pressure will build over northern California going into the weekend. Temperatures will trend warmer with dry conditions through at least Saturday.

Uncertainty works back into the forecast as another trough is projected to potentially reach the West Coast early next week. Stay tuned for forecast updates in regards to this next possible round of unsettled weather.