Light to moderate precipitation returns Saturday

March 6, 2020 – Dry today with above average temperatures. Precip chances return Saturday with accumulating snow and possible chain controls across the higher elevations.

Discussion

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High clouds are increasing across the area as the trough over the eastern Pacific approaches. Profiler data also indicate the marine layer has deepened to around 2500-3000 ft with stratus extending well inland across the Bay Area as onshore surface pressure gradients gradually increase. Current temperatures vary from the mid 30s in the colder mountain valleys, to the upper 40s to mid 50s across the Central Valley.

Upper ridge will continue to shift east today with the approach of the trough. Temperatures will continue to cool today as onshore flow picks up and clouds increase across, and will be only slightly above average for early March. Southwesterly breezes will pick up across the northern Sierra by the afternoon.

The trough will move through NorCal Saturday. This system will bring a quick shot of precip including moderate Sierra snow. Rainfall for valley locations will be heaviest over the northern Valley where 0.50 inches may fall, much less progressing south with only 0.10 inches over the southern Sacramento valley. Model trends have been wetter with this system and confidence is increasing. Snow levels will be somewhat low, down to 4500 feet, expect 4 to 8 inches above 4500 feet. Heaviest snow will occur during the day on Saturday, with possible chain controls during this time. Snow will diminish to light snow showers late Saturday night and Sunday with only light additional snow accumulation expected.

Extended Discussion (Tuesday through Friday)

A closed upper low off the coast of far Southern California continues to progress northeast on Tuesday. Ensemble guidance indicates this feature will continue to push towards southern California into Wednesday, before digging south towards the Baja Peninsula Wednesday night. The main bulk of precipitation looks to be over SoCal, although portions of the Sierra, surrounding foothills, and southern Sac Valley may see a few tenths of an inch on Tuesday. Weak ridging moves back over California Thursday nudging temperatures up a few degrees from previous days. Unsettled weather continues to look possible for the end of the week into the weekend.