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March 12, 2020 – Dry and warm weather today and Friday. Cold weather system will bring widespread rain and snow this weekend into next week with mountain travel impacts and low snow levels. Winter Storm Watch in effect from Saturday morning through Monday morning.

Discussion

Other than a few high clouds, skies are clear across the region early this morning. Current temperatures range from the mid 20s in the colder mountain valleys, to the upper 40s to mid 50s across the Central Valley.

Short-wave ridging moves over the area today, and combined with light to moderate northerly flow, very mild temperatures are expected with highs around 10-15 degrees above average.

Short wave riding breaks down on Friday ahead of a deep trough digging south from BC. Temperatures will cool around 5-10 degrees compared to today as flow reverses to onshore and synoptic cooling begins.

The trough closes off into a deep closed low by Friday night, and will drift slowly southward off the coast through the weekend. This pattern is often associated with significant precipitation and heavy mountain snow across NorCal.

Showers start to spread over the higher elevations late Friday night into Saturday morning as a cold front pushes south through the area. Precip will become more widespread Saturday evening as the trough axis drops south over us and we see strong vorticity advection. Mountain snow will become moderate to heavy at times with light to moderate valley rain. This will be a cold system with low snow levels generally in the 2500 to 3500 foot range.

Mountain travel will become difficult and hazardous starting Saturday and continuing into Monday with the potential for several feet of snowfall accumulation. If you have mountain travel plans this weekend you will want to plan accordingly and keep up to date with the latest forecast. High temperatures will be much cooler over the weekend running about 15-25 degrees cooler than forecasted highs on Friday and about 5-15 below average.

Extended Discussion (Monday through Thursday)

The long wave trough that will bring much needed precip to the region will slowly exit the region for the start of the work week. Showers are forecast to linger through much of Monday across interior NorCal with snow levels falling to around 2000 to 2500 feet. This could bring a light dusting of snow to the to those areas, but it looks to be short lived as snow levels are forecast to rise to about 3500 feet. As the trough exits the region, shower chances will decrease throughout the day on Tuesday. The best chance for additional rain and snow will be over the mountains and northern San Joaquin Valley at this time. High temperatures will continue to run cool about 5-15 below average through midweek.