January 26, 2021 – Freezing temperatures are expected across much the area this morning. A long duration, high impact winter storm this evening into Friday bringing periods of gusty winds and moderate to heavy rain and mountain snow. Potential for significant low elevation snow and damaging winds tonight and Wednesday as well as burn scar impacts to the LNU Complex and SCU Complex burn scars.
Discussion
We are in the calm before the storm early this morning as a short wave ridge builds in. This is bringing clear skies and with a cold air mass in place we are seeing cold temps this morning and the Hard Freeze Warning looks to be on track. Quiet weather is expected for much of the day today with increasing clouds.
The forecast will become very active starting in the evening as a trough drops out of the Gulf of Alaska. This will bring a high impact winter storm to NorCal. As the tough drops south we will see warm air advection increase over the region this afternoon into the evening with light precip developing over the Coastal Range after 1 pm. Precip will continue to overspread the area during the late afternoon into the evening. Precip will become heavier during the evening and will be the heaviest overnight as the cold front moves through. A NCFR (narrow cold frontal rainband) is likely to develop along the cold front and this will bring us the most intense rain and snow. This can be expected between 8 pm Tuesday and 8 am Wednesday and we could see rain rates exceed 0.50″ per hour and snow rates exceed 2″ per hour during this time. The best chances for the rain rain rates greater than 0.50″ per hour will be over western Yolo County into Solano County and south into western San Joaquin and Stanislaus County. This does include the LNU and SCU Lightning Complexes and a Flash Flood Watch has been issued for both of those burn scars.
The other big concern with this system will be the low snow levels. Snow levels will be 500 to 2000 feet this evening and will fall to the Valley floor over the northern Sacramento Valley overnight tonight into Wednesday morning. This will result in snow in Redding and Red Bluff with several inches expected. Snow levels will rise throughout the day Wednesday and we should see them rise above 3000 feet during the afternoon but they will remain locally down to 2000 feet over Shasta County.
Southerly winds increase rapidly overnight tonight as this storm moves in with 925mb NAM winds maxing out around 75 knots. This may translate to winds across the Valley of 35 to 45 mph with gusts of up to 50-65 mph. A High Wind Warning has been issued for these anticipated damaging winds. With widespread rain and heavy snow also anticipated during these overnight hours, expect extremely poor visibilities and hazardous travel conditions.
The back side of the trough will continue to dig down the CA Coast and that will help to stall the cold front over the region. This will keep rain and snow in the forecast for Wednesday and Thursday with the heaviest rain and snow expected from I-80 south.
Snow levels into Wednesday night will generally be between 3000 and 4000 feet locally lower over Shasta County. Snow levels on Thursday will continue to come up and we should see them rise to around 4000 feet by the afternoon. Light showers will linger into Thursday night especially over the higher elevations.
Extended discussion (Saturday through Tuesday)
Active storm pattern continues into early next week as an upper trough remains off the coast bringing persistent moist southwest flow into NorCal. Precipitation amounts likely to be significantly less than earlier in the week on Saturday giving a relative break to mountain travelers, but another round of impactful mountain snow looks likely Sunday into Monday.