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November 24, 2019 – Winter Storm Warning for Nevada County, Placer County, Yuba County and El Dorado County. Heavy snow expected. Travel will be very difficult to impossible. Tree branches could fall as well. Total snow accumulations of 2 to 3 feet, with localized amounts up to 4 feet at higher elevations, are expected.

Where: Motherlode and West Slope Northern Sierra Nevada including Interstate 80 at Donner Pass, Highway 50 at Echo Pass, Highway 88 at Carson Pass, Highway 4 at Ebbetts Pass, and Highway 108 at Sonora Pass.

When: Tuesday morning to Thursday afternoon.

A strong, unseasonably cold weather system is expected to bring the first significant winter storm of the season to Northern California, impacting the area Tuesday through Thanksgiving. Hazardous travel conditions with major travel impacts are expected over all NorCal mountain passes with this system, especially impacting holiday travel Tuesday night into Wednesday. Temperatures will also be colder than normal beginning Tuesday and continuing through the week.

Models indicate this system will move southeast from just off the western Canadian coast, deepening as it heads towards northern California on Tuesday. Precipitation is expected to begin on Tuesday afternoon, spreading southeast across the entire area by the evening hours. The low continues to strengthen Tuesday night which will lead to heavy rain and snow by Tuesday evening. Along with precipitation, models have trended significantly stronger with winds Tuesday night into late Wednesday morning across both the Valley and mountains. Valley winds may gust as high as 45 mph during this initial push of the system.

A High Wind Warning may need to be considered in future updates. Blowing snow and significant reductions in visibility during this timeframe will lead to extremely hazardous driving conditions and travel is highly discouraged during this time.

Overnight, cold air advection will drop snow levels significantly, especially in the Shasta County mountains and foothills. Have slightly lowered snow levels once more due to ensemble guidance indicating the potential for areas near Redding to see the potential for a few inches of snowfall. A rain snow mix may be possible in the city of Redding itself. Elsewhere, snow levels range around 2000 feet which would bring accumulating snow into the Sierra and coastal mountain foothills.

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The low makes its way overhead of NorCal on Wednesday and precipitation begins to become more scattered in nature Wednesday afternoon and evening, especially in the Valley. Models indicate enough instability to possibly generate a few storms in the Valley Wednesday afternoon, although confidence with this still remains low at this time for any specifics on location or timing. Continued snow showers mainly in the southern Cascades and Sierra will continue overnight on Wednesday with snow levels around 2000 feet, slightly lower in a few locations.

Extended Discussion (Thursday through Sunday)

Light to moderate rain and snow showers will extend into Thanksgiving Day. The low continues to be overhead this day only slightly shifting east by Thursday night. A few more inches of snow can be expected in the Sierra its foothills Thanksgiving into early Friday with snow levels around 2000 feet in the afternoon, dropping to near 1500 overnight. Even though snow will be lighter than previous day, hazardous travel will still be possible during this time. On top of the snow, another period of afternoon or evening convection may be possible on Thursday, especially if there is a but of clearing in the Valley.

The large, upper low finally shifts east on Friday although extremely light snow showers still look to be possible through early Saturday in the Sierra. On the tail of this previous storm, another system begins to make its way towards the west coast by late weekend which may bring additional precipitation to NorCal.

As for temperatures from Thanksgiving through next weekend, expect it to be chilly each day with below normal highs each afternoon. Low temperatures in the Valley dip into the 20s and 30s each night. Mountain locations should expect lows in the teens and 20s, with single digits possible in high mountain basins.