Winter storm will bring more Valley rain and heavy mountain snow through Monday with lingering showers Monday night. Isolated thunderstorm chances today and tomorrow. Locally gusty south to southwest ridgetop winds today. Cold and dry weather returns next week. Additional unsettled weather possible late week.

Discussion

Widespread precipitation has been observed across interior NorCal over the past 24 hours, as a major winter storm brings moderate rainfall and heavy mountain snow. Current radar shows two main bands of moisture impacting northern California this morning, with a break in precipitation in between. Patchy dense fog has developed in some areas this morning, such as Sac International Airport where rain has temporarily subsided and visibility has dropped to 1/8 SM. If you encounter fog, be sure to slow down and use low beam headlights.

24 hour rain totals vary throughout the Valley, with 0.15″ at KRDD, 1.75″ at Downtown Sacramento, and 0.74″ at KSCK. Portions of the Sierra foothills have observed higher amounts, with 2.31″ at KBLU and 2.21″ at KAUN.

Additional rain and heavy mountain snow are expected through tomorrow as the main low approaches the region.

Colder air associated with this low will allow for snow levels to continue to lower this morning, down to around 4,000 – 5,000 feet for the Sierra Nevada and 3,500 – 4,000 feet for the Shasta County mountains.

A Winter Weather Advisory remains in effect for the northern mountains and Burney Basin through 4 am PST Monday. A Winter Storm Warning remains in effect for the northern Sierra and mountains of western Plumas County and Lassen Park through 4 am PST Monday.

Locally gusty ridgetop winds are also expected today, out of the south to southwest direction, and strongest south of Highway 50 where ridgetop gusts 45 to 60 mph are possible.

Thunderstorms will also be possible with this system today, and again tomorrow late morning – early evening. Best chances are over the Sacramento Valley and Sierra foothills. Thunderstorms imply the potential for impacts such as lightning, small hail, gusty winds, and heavy rain.

Precipitation will taper off late Monday, with lingering shower chances overnight. Dry conditions return to the region by Tuesday and Wednesday as the low shifts eastward. Near to below freezing low temperatures are possible in the Valley on Wednesday morning, as the National Blend of Models currently has several patchy areas with a greater than 50 percent probability of 32 degrees or below.

Extended Discussion (Thursday through Sunday)

Ensemble guidance indicates another trough approaching the region late next week. There is still high uncertainty in the cluster analysis so confidence in timing and amounts for any precipitation potential late week and into the weekend is low.

The Extreme Forecast Index (EFI) continues to highlight areas of below normal daytime high and overnight low temperatures to continue for most of the extended forecast period.