February 20, 2019 – A weak, cold system moves through today into early Thursday with light mountain and foothill snow. Breezy winds Thursday with dry weather Friday. Light precipitation possible once again over the weekend and early next week.
Discussion
Mid level clouds cover most of the forecast area this morning ahead of a weak upper shortwave trough now over the northwest corner of the state. Cloud cover bringing warmer temperatures this morning with early morning temperatures anywhere from 4 to 10 degrees above 24 hours ago.
Radar is showing some light precipitation just west of Shasta county and models spread light precipitation southward across the forecast area today. Snow levels with this cold system will be quite low at around 2000 feet. As a result, snow ratios will be relatively high at 15:1 or more.
Therefore, even fairly light precipitation will translate to several inches of snowfall over the Sierra so will leave up winter weather advisory currently in place. Cooler airmass and cloud cover will bring cooler Max temperatures this afternoon. Precipitation will drop off late tonight as a secondary trough moves into SoCal. Main upper low forecast to move into the southern Great Basin on Thursday. The Sierra Cascade crest may see a few light showers under cyclonic flow but the remainder of the forecast area should remain dry on Thursday with a little warming. Northerly flow between upper low over southern Great Basin and high pressure ridge over the eastern Pacific will bring breezy north winds Thursday afternoon and evening.
High pressure pushing in over the state will bring fair skies and warmer temperatures on Friday. Mainly clear skies and lessening wind will allow morning lows Friday to cool again with near freezing temperatures returning to the central valley. Still should be enough wind around, however, to keep temperatures from dropping to much below freezing. Mainly fair skies will continue into Friday night but warming airmass should keep morning lows Saturday elevated above Friday morning lows.
An upper trough digging out of the Gulf of Alaska and down the west coast is forecast by models to start bringing precipitation to the northern forecast area by Saturday afternoon. Forecast models show fairly light precipitation dropping southward over the region as the upper low shifts slowly southward. Forecast models keep this trough of low pressure stretched out over the Pacific northwest going into early next week for a continued threat of light precipitation with relatively low snow levels remaining over the region.
Extended Discussion (Sunday through Wednesday)
A weak system moves through Sunday, bringing light Valley rainfall and a few inches of mountain snow. Snow levels should be around 2000-3000 feet.
Models trending towards nearly stationary frontal boundary with precipitation continuing into early next week and potentially beyond. Confidence in details remains low for now. Will keep unsettled pattern continuing through next week.