Rain and Mountain Snow through Saturday – more on the way

March 13, 2018 – Series of Pacific storms will move through this week bringing periods of rain and mountain snow, heavy at times and gusty wind.

Discussion

A few lines of showers have moved across the area overnight in the warm sector ahead of the approaching cold front. Snow levels have remained high – above 8000 feet – and Caltrans traffic cameras show only rain across the northern Sierra passes. Winds have also picked up across the Sacramento Valley as surface pressure gradients have tightened considerably (SAC-MFR now approaching 11 mbs) with gusts over 30 mph now being reported at Redding and Red Bluff. Temperatures are very mild ranging from mostly the 40s in the mountains to the upper 50s to mid 60s across the Central Valley.

The cold front will move through NorCal today accompanied by more widespread precipitation. Winds will remain gusty out of the South ahead of the front this morning, but will subside some this afternoon. Most of the precipitation will occur today in the valley, but will continue through Wednesday across the northern Sierra with moist upslope flow and steep lapse rates remaining in place in the post-frontal environment. Snow levels will lower below pass levels this afternoon as colder air is ushered in.

Precip amounts with this first storm look to be around a half inch to about an inch in the Central Valley, highest in the northern Sacramento Valley with 1.5 to 3 inches in the foothills and mountains. Snow amounts of 1 to 3 feet possible by Wednesday at pass levels with 12-18 inches down to around 5000 feet.

Showers look to taper off somewhat in the Central Valley tonight and Wednesday while continuing in the Sierra Nevada, though a risk for showers and thunderstorms will continue. Small hail expected to be the main threat with valley thunderstorms.

Models show somewhat of a break Wednesday night into Thursday before precipitation increases again. An additional 1 to 1.5 inches of rain expected in the Central Valley. Moderate to heavy snow will return across the mountains of Western Plumas county and the Sierra Nevada. GEFS and SREF plumes are indicating an average of around 2 feet of snowfall for KBLU by 12Z Saturday, and some of the higher terrain may see 7 feet or more by the weekend. Winter storm warning in effect with additional warnings likely through Friday.

Extended discussion (Saturday through Tuesday)

Light precipitation may continue across the region into Saturday as a weak shortwave trough passes through the region. A brief period of drier weather then ensues Sunday or Monday as a high pressure ridge quickly passes through the West Coast.

Though there are still discrepancies, the GFS and ECMWF have come into better agreement with the handling of the next storm system: a closed upper low slowly approaching California. The first wave of precipitation with this system is now expected to arrive on Tuesday. The ECMWF brings this system inland over NorCal, and the GFS over SoCal, these solutions would offer far different QPF values across the region. Regardless, confidence is high that the unsettled weather pattern will continue through at least the middle of next week.