Next wave of storm pushes south across the entire area today continuing periods of rain, mountain snow, and gusty southerly winds with rising snow levels and isolated thunderstorms through tonight. The second, colder wave of the storm moves onshore Saturday through Tuesday bringing additional periods of rain and moderate to heavy mountain snow with isolated thunderstorm potential. Lower snow levels with this next wave introduces potential for up to a few feet of snow at pass level.
- Winter Storm Warning: From 4 PM Today through 4 PM Tuesday for elevations above 6000 feet along the Sierra/ Southern Cascades including Interstate 80 and Highway 50.
- Flood Watch: Through 4 AM Saturday for Valley/foothills locations generally north Interstate 80 and below 3000 feet.
- Wind Advisory: Until 10 AM Friday for the Northern/Central Sacramento Valley and Northeast foothills.
Discussion
Bands of moderate to heavy precipitation continue to progress inland early this morning primarily north of I-80 as seen on RADAR. Hourly precipitation rates are between 0.15″ to 0.3″ over the Coastal Range and Sierra foothills. High-resolution convective models depict precipitation moving over the Coastal Range, northern/central Sacramento Valley, and northern Sierra early this morning, before crossing over the I-80 corridor by around 5-7 AM. Valley locations will primarily see scattered showers, with isolated areas of moderate to heavy rainfall and gusty winds with more organized bands of precipitation. Southerly winds are currently gusting 30 to 40 mph around the northeastern Sierra foothills and central Sacramento Valley. Winds will be strongest this morning, with gusts 40 to 50 mph possible across the aforementioned area. BM probabilities of gusts stronger than 50 MPH are 50-70% across eastern Tehama County. As a result the Wind Advisory remains in effect through 10 AM today. Winds are expected to weaken heading into the afternoon, with periodic gusts 25 to 35 mph.
As precipitation pushes further south and east and sliding eastward across Northern CA today, with lingering showers over the mountains on Saturday. Active weather reinvigorates on Sunday evening into early next week as our low pressure system in the Pacific NW continues troughing over Northern CA bringing continued rain and mountain snow impacts through Tuesday morning.
Our Winter Storm Warning is in effect for 4 PM today until 4 PM Tuesday when waves of heavy snow are expected to produce accumulations of 1 to 4 feet, up to 5 feet along the higher peaks. The first wave of moderate to heavy snow will move through later this afternoon continuing into Saturday afternoon. A secondary wave moves through Sunday night into Tuesday afternoon. Lingering scattered snow showers will be present in between these two waves, resulting in a brief break or continued, lower- intensity snowfall for areas in the Sierra. Snow levels will initially be around 6000 to 7000 feet today, lowering to 4500-5500 feet over the weekend. Monday will see minor rises in snow levels with 5000-6500 feet expected. Lastly, winds will also gusts up to 50 MPH.
Also, with this system will see periods of moderate to heavy rain across the Valley through early next week. Similar to snow, there will be waves of heavier precipitation over the next several days with the highest amounts over the mountains, then foothills, and lastly the Valley floor. The mountains will see anywhere from 5 inches to 1 foot of precipitation through Tuesday, heaviest near the Feather River Valley. The foothills will see 5 to 9 inches, increasing as you move northward and approach the Feather R. Valley. Lastly, the Valley will see 1.50 to 4 inches, heaviest over the Northern Sacramento Valley.
As a result, a Flood Watch remains in effect for the northern half of the Central Valley for excessive runoff resulting in sharp rises in rivers, creeks, and streams, and ponding of water or flooding on roadways and other low-lying locations. For the mountains and foothills north of Hwy. 50, chances for totals greater than 4 inches is 50-90% between today and Monday afternoon. For the Valley, there is A 50-80% chance of totals greater than 3″ from today to Monday afternoon. From this late morning through Saturday, there is a 10-20% chance of thunderstorm development, primarily from the Northern Sac. Valley to the eastern portions of the Valley north of Interstate 80.
Extended Discussion (Tuesday through Friday)
Ensemble guidance indicates that the upper level trough continues to move inland on Tuesday, bringing continued rain and mountain snow to interior Northern California. The Winter Storm Warning remains in effect through 4 PM PST Tuesday above 5500 feet as mountain snow showers continue through much of the day. The National Blend of Models (NBM) suggests a 45-75% probability of snow amounts of 6 inches or more from Tuesday through Tuesday night across the Sierra Nevada. Snow levels are expected to be around 4500-5500 feet for most of Tuesday, lowering to around 4000-5000 feet Wednesday morning.
Rain showers at the lower elevations are expected over a similar period, with the NBM suggesting a 35-65% probability of a quarter of an inch of precipitation or more in the Valley and foothills from Tuesday through Tuesday night. A few lingering showers and mountain snow showers will be possible on Wednesday, although there is still some uncertainty on timing of showers tapering off vs persisting over the midweek timeframe. With ensembles indicating some upper level ridging building in offshore of the Pacific Northwest / Gulf of Alaska behind the trough in the middle of next week, a relatively drier and quieter Thanksgiving Day is possible. Be sure to stay up to with the latest forecast at weather.gov/sto if you have outdoor holiday plans and check current road conditions at quickmap.dot.ca.gov before traveling!