January 28, 2021 – A long duration, high impact winter storm will continue to impact the region through Friday. Periods of gusty winds, moderate to heavy rain and blizzard conditions over the Northern Sierra. Potential for burn scar impacts to the LNU Complex and SCU Complex burn scars today.
Discussion
Rainfall and mountain snow will continue today. Snow levels will be higher than yesterday so no valley or foothill snow is expected but additional significant snowfall is still expected over the western slopes generally in the 3500 to 4500 foot level during the day. Snow levels will be around 2000 to 2500 feet over Shasta County with less snowfall expected so have downgraded the Warning to Advisory. Some local cold spots may get some snow down to around 1500 feet.
Winds are a lot lighter than yesterday but will still be breezy during the day. Have added some thunderstorm chances into the forecast for this afternoon and evening over on the western side of the valley and Delta. That was enough to keep the Flash Flood Watch for the burn scares going through today. Any thunderstorms that develop look like they would contain heavy rain and small hail.
The system will be winding down over the valley this evening and the mountains late tonight. Some lingering showers are expected on Friday but nothing of significance. Friday night and Saturday will be mostly dry everywhere with the exception of western Shasta County and the northern portions of the interior mountains.
On Saturday a weak wave moves near the area that may bring a few showers to the above mentioned area. We will see increasing chances for some precipitation late Saturday night and Sunday for mainly areas north of I-80 with areas to the south staying dry.
Extended discussion (Monday through Thursday)
We will see a wet start to the extended period as an upper level trough drops south into the region. The WPC clusters would indicate that ensembles overall are in very good agreement with the placement and timing of this system. Warm air advection will bring precip for the start of the period with a cold front pushing through NorCal during the day on Monday.
This system will be able to tap into a higher moisture and is looking to fall in between 250 and 500 on the IVT Magnitude. It will not be nearly as wet as this last system but it will bring light to moderate rain to the Valley and moderate to heavy snow to the mountains. The cold front will clear the area on Monday with the trough axis swinging through on Tuesday. This will keep showers in the forecast into Tuesday night. Snow levels start out 4500-5500 feet with this system and will fall to 2500-3500 feet behind the cold front Monday night.
Mountain travel will likely be the main impact with this system but we can expected increased southerly flow ahead of the cold front but at this point the winds don’t look very impactful.
Upper level ridging builds in on Wednesday and this will bring a quiet end to the extended period. Highs will start out a bit below average but will warm to near average by the end of next week.