March 1, 2018 – Heavy snow and gusty winds will impact the foothills and mountains with heavy rain showers, gusty winds and isolated thunderstorms over the valley today into the weekend. A brief drying out period early next week will be followed by another shot of precipitation mid week. Winter Storm Warning until 10 PM Saturday, Wind Advisory until 8 PM this evening.
Discussion
Precipitation now falling over nearly all of the CWA as a Pacific Cold front makes its way across the north state. IR satellite image indicates that the back edge of this front is now moving on to the north coast.
Precipitation amounts so far have ranged from about one quarter to three quarters of an inch. Pre frontal winds are topping 20 knots over the central and northern Sacramento valley with lighter but still breezy winds farther south. Stronger winds should continue to track farther south as the cold front progresses so wind advisory still looks on track.
Snow levels this morning range from around 2000 to 2500 feet over Shasta county to around 4000 feet over the northern Sierra. Locally lower snow levels have been reported over Shasta county where cold air is trapped in the Sacramento canyon north of Shasta Lake. Web cams show slushy snow down to Lakehead at 1200 feet but snow levels should rise a bit later this morning as the cold air is mixed out. Therefore, current winter storm warning for levels above 2000 feet still looks okay.
Main cold front shifts into the northern Sierra this evening with winds expected to decrease slowly behind the front overnight. Daytime highs today will continue to fall in the cold air with and behind the front remaining below normal. Depending on timing of front, afternoon valley thunderstorms will be a possibility if there is enough clearing.
Heavy snowfall will continue tonight over the Sierra Cascade range as this first cold front moves through. A secondary shortwave moving through NorCal tonight will bring another round of heavier precipitation during the night as well as colder air and still lower snow levels Friday morning. The Redding area in the northern Sacramento valley could see a little bit of snowfall but snow levels should rise some during the day with daytime heating. Valley thunderstorms will again be a possibility Friday afternoon as subsequent shortwaves associated with the main upper low pivot through the north state.
The main upper trough axis shifts into norcal on Saturday bringing continued showers. Snow levels will remain quite low so mountain travel impacts will continue one more day. Stability progs indicate enough instability for afternoon thunderstorms again so added valley thunderstorm threat for one more day. ECMWF a little slower in moving the upper trough east of the region on Sunday but most locations should turn dry on Sunday as upper ridge pushes in and northwest flow aloft develops. Have left a slight shower threat over the northern zones however to account for slower ECMWF model.
Extended discussion (Monday through Thursday)
Dry weather expected Monday and Tuesday of next week as upper level ridging moves through. Forecast becomes less clear beyond this time frame as models diverge with solutions. While EC keeps ridging over the area through early Thursday, GFS20 is much more progressive and pushes next Pacific storm into the forecast area midweek. At this time, forecast leans more towards the GFS20 given present wetter pattern.