A strong weather system will bring precipitation impacts, strong southerly winds, and thunderstorm potential through Saturday. The heaviest precipitation is expected tonight into Saturday morning. Predominantly dry weather on Sunday, followed by a weaker system on Monday that will bring additional precipitation impacts. Periods of moderate to heavy rainfall will lead to sharp rises on creeks, streams, and rivers with nuisance roadway flooding.
Looking at webcams, snow rates have tapered off with little in additional accumulation expected early this morning. As a result, our Winter Weather Advisory for the Sierra and mountains of Shasta County has been cancelled. There will be lingering snow showers with continued chain controls, so please continue to exercise caution if attempting mountainous travel.
Precipitation reports show around 0.50-1.50″ in the Valley and 0.10-1.00″ over the mountains in the last 24 hours. We will see a brief lull in heavier precipitation for the next several hours with the next wave looking to move from west to east beginning around 6-8 AM this morning. This wave will last until SAturday afternoon with lingering snow showers over the Sierra through the evening. Friday night into Saturday late morning will be the heaviest period of precipitation with things winding down by Sunday morning. Valley forecasted totals with this wave are 0.75-2.25″ north of I-80, and 0.10-0.75″ southward. The foothills are 0.75-3.00, up to 4″ with the mountains 2.00-6.00″, up to 8 inches along the Coastal Range and the Feather River Canyon areas. In the Central Valley, the NBM shows a 40-80% chance of amounts greater than 1.50″ from this morning through Sunday morning. For the mountains and foothills, there is a 50-85% chance of amounts greater than 3 inches for the same timeframe. As you move further north and up in elevation, amounts can be expected to increase.
Periods of moderate to heavy snow will also accompany this weather system. Lingering snow showers continue across parts of the Sierra with snow redeveloping in earnest, first along the Coastal Range this morning and to the Cascades and Sierra by morning’s end. This will continue through Saturday evening, tapering off overnight into Sunday morning. Snow levels will generally be 4500 to 5500 feet As a result, Winter Storm Warnings have been issued for Shasta County mountains, Southern Cascades, and Sierra.
For Shasta County, 8 to 24 inches is forecasted above 3500 feet, locally higher along the peaks with wind gusts as high as 45 MPH. For the Southern Cascades/Sierra, 1 to 3 feet above 5000 feet is expected, locally higher along the Sierra crest with gusts up to 50 MPH. Models show a 50-80% chance of amounts greater than 2 feet over the Sierra, highest north of I-80. The heaviest period of snow will be Friday night into Saturday late morning over the Sierra and Southern Cascades. Snow covered and slippery roads, chain controls, and reduced visibilities will contribute to travel delays and could become very difficult. Check the latest road conditions from CalTrans online at quickmap.dot.ca.gov or dial 511.
Lastly, Friday late morning gusty winds begin to form with gusts of 20-45 MPH, expected from Friday afternoon to Saturday late evening. The strongest winds will be across the northeastern foothills first Friday evening with the Delta joining in Saturday morning. Saturday afternoon will see the winds begin to trickle out and becoming light by Sunday morning. NBM probabilities have a 60-95% chance of gusts stronger than 40 MPH, strongest over the foothills and Delta. As a result, a Wind Advisory is in effect from 10 PM Friday to Noon Saturday for southeast winds 15 to 25 mph and gusts of 45 to 50 MPH expected over the Sacramento and Northern San Joaquin Valleys.
Sunday morning will see the active weather ending, with dry weather expected by daybreak. Mostly sunny conditions and light winds are expected. The next round of active weather begins on Monday late morning, though this system will be quick and not nearly as strong. Current snow amounts of around 4 to 10 inches are forecasted for above 6000 feet, up to 12 inches near Lassen NP. Rain with this wave will be considerably less with only 0.10-0.50″ forecasted for the Valley and 0.25-1.25″ over the foothills and mountain areas. Snow levels will be between 3000-5000 feet on Monday, rising to 4500-5500 feet Tuesday morning.
Extended Discussion (Tuesday through Friday)
Clusters and ensembles are in good agreement regarding another quick-moving system moving through the region on Monday. This system does look to be weaker compared to the weekend system. Widespread precipitation and accumulating mountain snowfall are expected.
The National Blend of Models (NBM) indicates a 30 to 60% chance of a half inch or more of rain north of I-80, with up to 70% in the mountains. Snow levels will be between 3500-5000 feet on Monday, rising to 4500-5500 feet Tuesday morning. The NBM projects a 40 to 70% chance of 6 inches or more in the Sierra on Monday. A few lingering snow showers will be possible over the mountains Tuesday morning, before drier weather prevails Tuesday through the remainder of the extended period.