Lingering showers and mountain snow showers today, with cooler high temperatures. Short break in activity through Tuesday morning, then another wave of active weather enters the region bringing renewed chances for light Valley rain and mountain snow through Thursday.
Discussion
Some lingering snow showers in the Sierra and light Valley and foothill rain showers persist on radar this morning. Activity is expected to continue winding down as we approach sunrise. At the time of this writing, chain controls were still up along I-80, US49, US50, and US88, so we are letting the Winter Weather Advisory continue until snow shower activity ends and chain control restrictions are eased/lifted. Outside of a few wrap- around showers and mountain snow showers today, most of the area should see relatively quiet weather and some clearing.
Looking at 500mb heights this morning shows an area of low pressure over central and eastern Nevada, and is forecast to continue to translate eastward throughout the day. Upper level ridging is then forecast to build offshore and move inland by Tuesday, leading to further clearing skies early in the day. The break in active weather will be relatively short, as another short-wave trough is forecast to move into the region later Tuesday night and Wednesday morning. A modest plume of around 250 kg/m/s IVT will move into central/southern California as the trough is moving through NorCal. With this setup, areas south of I-80, the foothills/mountains will stand to receive the most precipitation. National Blend of Models (NBM) probabilities for 0.50″ inches from Tuesday night through Thursday is around 50-90% in the mountains/foothills of the Sierra and southern Cascades, around 10-30% in the Valley and Delta. Little to no impacts are expected due to rain from this second wave.
Snow totals have trended slightly higher again this morning, with the NBM is showing around a 60-80% chance of 6 inches of snow above 5000 feet and 40-70% for 10 inches of snow above 6000 feet. Snow levels are trending around 5000-6000 feet at onset, then lowering to around 3500-4500 feet by Thursday AM. Forecast impacts include snow covered roads in the higher elevations, chain controls, and travel delays, very similar to our recent system. Consideration will be given later this morning to issuing another winter weather product to cover the next system.
Temperatures will be below normal through Thursday as well with the transient ridge developing tomorrow and the impending trough by Tuesday night and Wednesday. Highs in the Valley are forecast to be in the upper 50s to low 60s, with cooler low 30s to mid 40s for our higher elevations.
Extended Discussion (Friday through Monday)
By Friday, ridging begins to dominate the forecast pattern as heights rise from northwest to southeast. Current forecast projects a break in active weather on Friday with another round of rain, mountain snow, and breezy winds on Sunday into the following week. Friday and Saturday will see breezy north winds up to 15-20 MPH throughout the Central Valley with NBM probs showing a 25-40% chance of gusts stronger than 25 MPH and Saturday’s winds will be more confined to the northern half of our forecast area. Over the mountains, we can expect gusts up to 25-30 MPH.
There is around an 50-80% chance of accumulations greater than half an inch Sunday into Monday, up to 85% from Hwy. 50 to south of Lassen NP. Recent runs have Sunday afternoon and evening being the wettest period of the extended forecast with most impacts focused on the mountains and adjacent foothills areas. There is a local area of elevated precipitation over the Southern Cascades areas and north-central Shasta County that if showers develop any further west, we may see rain impacts as far west as Redding and Red Bluff but that is a low probability outcome at this time.
We’ll continue to monitor trends in the forecast as we progress through the week, but at the moment it looks like we’ll see continued weak systems move through Northern California towards the end of the second week of March.