Rain showers and isolated thunderstorms brought some heavy snow to the Sierra Nevada into the evening. The second weather system will bring periods of moderate to very heavy snow in the mountains and widespread moderate to heavy rain with gusty winds from the south in the valleys.
discussion
Showers continue in the Valley, with isolated thunderstorms possible across the Central Valley in the afternoon and evening. The highest potential for convection is in the foothills toward Redding. When thunderstorms develop, the main threats are short periods of heavy rain and small hail.
In addition, light to moderate snow is expected in the Sierra Nevada above approximately 3,500 feet through tonight, with scattered snow showers and the potential for heavy snow at times. Please use caution when traveling today and check the latest road conditions. Overall, precipitation will decrease on Saturday except for some light snow in the mountains.
Our attention shifts from early Sunday morning into Tuesday morning as the next atmospheric river impacts Northern California. A winter storm warning for heavy to very heavy snow above 4,500 feet was issued for western Plumas County/Lassen Park and the northern Sierra Nevada West Slope from Sunday morning through Tuesday morning.
Snow totals are expected to be 2 to 4 feet, with 5 to 6 feet at mountain peaks. This system allows for extremely difficult or impossible movements due to travel delays, snow-covered roads, reduced visibility, etc. that can result in chain controls and road closures.
Snowfall chances are consistent with the nature of this system's higher snow totals, with a 60-100% chance of 24 inches or more above 6000 feet. Between 4500 feet and 6000 feet, there is a 40-90% chance of 12 inches or more. The heaviest snow will be on Sunday, especially Sunday morning.
Snow levels will initially be 3,000 to 4,000 feet, increasing to 4,000 to 6,000 feet by Sunday afternoon and settling at 4,000 to 5,000 feet by Monday.
In addition, a winter storm warning was issued for the Shasta Lake area, northern Shasta County, and the entire Coastal Range from Sunday morning into early Monday morning. Heavy snow is expected above 3,500 feet, including high-elevation Interstate 5, and 2 to 5 inches below 3,500 feet. Snow-covered roads may be subject to chain restrictions or road closures, making travel difficult. The chance of snow accumulation is 40-80% of 12 inches or more above 3500 feet, but only 25-50% chance of 4 inches or more below 3500 feet. Similarly, the heaviest snowfall will be on Sunday.
Snow accumulations in the Coast Range and northern Sacramento Valley will range from 2,000 to 3,000 feet, increasing to 3,000 to 4,000 feet by Monday morning.
Rain will enter the valley from the southwest late Saturday night and spread north across the valley. Forecast totals from Saturday night through Tuesday morning are 1.75 to 3.00 inches in the Valley, highest in the central Sacramento Valley.
2.00 to 4.00 inches will be observed in the foothills, with the highest near Chico. Sunday morning will be the wettest period, with moderate to heavy rain expected Sunday and Monday. There is a 30-60% chance of 2 inches or more and a 65-90% chance of 1 inch or more.
Strong winds will move through the valley late Saturday night into Sunday. South to east winds will move through the valley at 25 to 35 mph, with gusts as high as 40 to 50 mph. Winds will be strongest Sunday morning and taper off in the afternoon and evening. Strong winds can blow around unsafe objects, making it difficult for large vehicles to navigate.
There's another chance of thunderstorms (10-15%) Sunday from I-80 to Chico, then Monday (10-20%) from southern Sacramento County to northern San Joaquin. The main threat from this is short periods of heavy rain and small hail. Be sure to check the latest forecast for any changes to the forecast.
Extended discussion (Tuesday to Friday)
Ensemble and cluster analysis confirm that the main low-pressure center responsible for the high-impact weather Sunday through Tuesday will propagate eastward, resulting in moisture remaining at the trailing edge of the low. As a result, showers will remain in the valleys and foothills for some time on Tuesday afternoon, and snow will fall in the mountains.
The National Blend of Models gives less than a 20% chance of rain of 0.50 inches or more in the valley and a 30-50% chance in the foothills.
Additionally, the Sierra Nevada and Southern Cascades have a 40-60% chance of receiving 2.00 inches or more of snow at elevations above 5,000 feet. By Wednesday, afternoon weather in the valley is expected to be mostly dry, with continued showers in the foothills and mountains. Precipitation will be less than 0.25 inches, with less than 1 inch of snow in the mountains. The impact is expected to be minimal, if any.
A weaker shortwave trough will move through the region Thursday into Friday, bringing light to moderate rain to the valley and potentially several inches of snow to the mountains. The NBM has a less than 20% chance of 0.50 inches or more of rain in the valleys and a 30-50% chance of 2.00 inches or more of snow in the mountains.
Given the potential for destruction by this system, the exact details are unknown at this time. However, its strength will be significantly weaker when compared to the forecast for the upcoming atmospheric rivers affecting the region from Sunday to Tuesday.
