NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 220013
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
413 PM PST Wed Feb 21 2018

.SYNOPSIS  
A cold system will bring low elevation snow to the mountains late tonight into early Friday, which could impact travelers. Below normal temperatures will continue. Additional systems possible next week.
.DISCUSSION  A cold system dropping south from western Canada will bring low elevation snow to NorCal Late tonight into Thursday night. Snow levels will be around 2000 feet, but briefly fall to 1000 feet at times in heavier snow showers. The system has slowed a bit and have pushed back the start time for the winter weather advisory to after midnight. Snow amounts of 3 to 6 inches are expected above 2000 feet with local amounts up to 10 inches over higher peaks. Foothill locations like Grass Valley...  Placerville and Sonora can expect 2 to 4 inches. Locations like Auburn and Jackson could even pick up a quick dusting. Unstable air will move over the area Thursday afternoon with thunderstorms possible over the valley some with small hail. This convective activity will also enhance snow as it moves into the foothills and mountains late in the afternoon. The system will move east of the area Thursday night with snow ending around midnight. A brief period of dry weather is expected Friday as short wave ridge moves overhead between systems. The next system will drop south in the northwest flow Saturday with a quick 1 to 3 inches of snow for the Sierra north of highway 50.
.EXTENDED DISCUSSION  (Sunday THROUGH Wednesday)  Active pattern is expected through the extended period as successive disturbances embedded in the upper flow drop down from the north. Guidance is still struggling with the progression of these systems and precipitation amounts. Regardless, these systems have the potential to bring widespread precipitation, mountain snow, and breezy to gusty winds. Given the cold nature of these systems, snow levels will remain relatively low. Unlike previous systems, the upcoming ones have the potential to pull in significant moisture. At this point, Sunday appears to be dry except for shower activity over the mountains. More widespread precipitation is possible across the forecast area Monday into early Tuesday. After a brief break late Tuesday into early Thursday, a stronger and wetter system is progged to push across interior NorCal late next week, but details remain uncertain. Temperatures will remain at or below average.
.AVIATION 
VFR conditions this evening. MVFR/IFR due to snow showers over the foothills/mountains, mainly after 08z Thursday. Isolated thunderstorms in the Central Valley after 18z Thursday.
.STO   WATCHES/WARNINGS/ADVISORIES    
Winter Weather Advisory from 1 AM to 10 PM PST Thursday for Burney Basin / Eastern Shasta County-Motherlode-Northeast Foothills/Sacramento Valley-West Slope Northern Sierra Nevada- Western Plumas County/Lassen Park.
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