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December 15, 2016 – Wet and windy weather with high-elevation snow today and tonight. Showers ending over the Sierra on Friday. Freezing temperatures in the valley this weekend with dry conditions. Mainly dry next week except for a slight threat of light showers northern mountains mid week.

Discussion

Pacific frontal system now moving onto the north coast bringing moderate rainfall to the coast range and northern Sacramento valley. Beale radar one hour rainfall estimates even showing a few isolated locations in the coast range between .3 and .5 inches per hour. Models continue to show this as a very moist storm with TPW values around 1.5 inches just off the coast. Ahead of the front, surface pressure gradient of nearly 8 mb from MFR to SAC bringing gusty winds to the northern and central Sacramento valley. For the most part, kept morning forecast package mainly in line with previous forecasts. Main change was a slight slow down in frontal progression inland. For this reason, slowed progression of wind advisory winds southward.

Also upgraded the winter storm watch to a warning for northern Sierra zones and raised warning snow levels as it appears no significant snowfall will occur after snow levels drop to 5000 feet on Friday. Latest timing shows frontal band moving into the northern Sacramento valley by late morning, the southern Sacramento valley by late this afternoon and into the Sierra by this evening coinciding with periods of heaviest precipitation at these locations.

Eastern Butte county will be area to watch today with orograhics and moisture making this area of significant rainfall. WPC will issue moderate risk for excessive rainfall for this area.

Precipitation will continue over the Sierra much of the night while decreasing elsewhere behind the front. Upper troughing will allow for continued shower threat over the Sierra Cascade range on Friday but elsewhere should remain dry Friday with daytime temperatures on the cool side in cold air behind the front.

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Weather clears out Friday night as upper ridging develops over the eastern Pacific and northerly winds develop. Clear skies and cold airmass will allow overnight lows throughout the central valley to drop to near or below freezing.

High surface moisture may allow for some fog to form as well especially southern Sacramento and northern San Joaquin valleys where winds should be a little lighter. Sunny skies Saturday will allow for a little warming some areas but cold airmass will keep highs below normal. Sunny skies and continued breezy north winds are expected on Sunday with a little warming but daytime highs are still expected to remain below normal.

Extended Discussion (Monday through Thursday)

Upper ridging continues over NorCal Monday with locally gusty easterly wind over the Sierra Nevada in the morning. High temperatures expected to be just slightly below normal with mainly lower 50s in the Central Valley. Short wave trough pushes through the PacNW Tuesday with southern portions moving across the northern part of California. Models differ with depth of wave and timing, leading to uncertainty in POPs Tuesday. For now, have some slight chances mentioned over our coastal mountains and northern portions of the CWA. Short wave upper ridging moves through Wednesday for dry weather then models diverge significantly with another possible short wave trough Thursday.

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