November 19, 2019 – Pattern change begins today to breezy to windy conditions, cooler temperatures and possible showers over mainly the Sierra Nevada south of I-80.
Red Flag Warning from 4 AM Wednesday to 7 AM PST Thursday for Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 feet. Winter Weather Advisory from 4 PM this afternoon to 7 PM PST Wednesday for West Slope Northern Sierra Nevada.
A band of high clouds associated with the upper level front is pushing southeastward into central California early this morning while the surface front is making its way into northwest California. Current temperatures are milder across most of the area compared to 24 hours ago and range from the upper 30s to mid 40s in the mountain valleys to the 50s across the Central Valley and milder foothill and mountain thermal belts.
The initial portion of the trough will dig southward off the coast this morning, while the stronger wave (presently along the BC coast) will rapidly drop south today before closing off near Monterey later tonight. The entire system will move south into SoCal on Wednesday, then another batch of energy is forecast to drop into the region on Thursday into Friday.
While some showers may begin as early as this afternoon across the northern Sierra, the main impact from the system will be cooler temperatures and an increase in northerly wind that will develop across a large part of the area later today and continue into Thursday as surface gradients tighten.
The period of strongest northerly winds is expected Wednesday afternoon as subsidence and upper level support increase. Gusts of 40-50 mph will be possible in the Sacramento Valley and surrounding terrain north of Sacramento.
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Showers chances will be concentrated in the northern Sierra to the south of Tahoe tonight into early Thursday where snowfall accumulations of 1-3 inches with local accumulations up to 8 inches will be possible across the higher elevations. This will cause some travel issues over some of the high Sierra passes and a Snow Advisory has been issued.
Extended Discussion (Saturday through Tuesday)
Upper ridging over northern California will allow for quiet weather over the weekend with light winds and slightly warmer than normal highs each afternoon. The main period to watch will be early next week as a system drops into the western/central US. Ensemble guidance suggests this system digging into Central Great Basin Monday night bringing the potential for another strong north wind event. With dry conditions forecast, elevated fire concerns may be seen. Ridging continues through at least Tuesday, although this may break down by mid-week.