Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 132200

Area Forecast Discussion
National Weather Service Sacramento CA
300 PM PDT Tue Mar 13 2018

Series of Pacific storms will move through this week bringing
periods of rain and mountain snow, heavy at times, with gusty
wind and thunderstorms.


Pacific frontal system moving into the eastern foothills and
mountains this afternoon. Lines of stronger returns are being
observed on 88D Mosaic with embedded thunderstorms extending from
the West Slopes of the Northern Sierra Nevada through the
Motherlode, into the San Joaquin Valley. HRRR showing heavier
precip continuing in the Motherlode and Sierra throughout most of
the night. Snow level radar indicating snow level above 8000 feet
at Colfax but is lowering at Chico and Oroville to 5700 feet as
colder air is ushered in behind front. Expect snow levels to drop
below pass levels this evening, then continue to lower overnight
to 3500 to 4500 feet by Wednesday morning. Periods of heavy snow
and strong wind expected in the Sierra overnight.

Showers continue over Interior NorCal Wednesday as upper level
trough moves through. Periods of moderate snow showers expected in
the Sierra Wednesday. Models showing significant amount of CAPE
at the lower elevations tomorrow afternoon to include
thunderstorms in the forecast. Stronger storms likely to produce
some hail.

Upper trough shifts through Wednesday night with showers
decreasing overnight into early Thursday. Models then show
channeled vort moving into the area Thursday afternoon into night.
Snow expected to ramp up in the mountains Thursday afternoon into
night. Main upper low digs along the NW CA coast Friday with
additional waves rotating into the area. Showers and thunderstorms
likely Friday with continued periods of heavy snow in the
mountains. Snow levels continue around 3000 to 4000 feet, but
could be down to 2500 feet in heavier convection. Have added
Winter Storm Watch for this next system. Snow advisories may also
be needed for the Coastal and Shasta mountains late Thursday and



Precipitation could continue across interior NorCal on Saturday
as a weak upper disturbance pushes through the area. Drier weather
will return Sunday into early Monday as ridging attempts to

Active pattern returns early next week as an upper level system
drops down into the Eastern Pacific and move into the West Coast.
However, there are model differences in timing and evolution of
this system. The GFS begins to spread precipitation as early as
Monday afternoon, while the ECMWF holds off until Monday evening.
In addition, the GFS digs the upper system southward and ends
precipitation faster than the ECMWF. Regardless, confidence is
high that the unsettled weather pattern will continue through at
least the middle of next week.


Storm system will continue to bring MVFR/IFR conditions across
Valley TAF sites, and IFR/LIFR conditions over the mountains.
South winds 10-20 kt with gusts to 30 kt across the Valley will
continue through 01z Wednesday.


Winter Storm Warning until 5 PM PDT Wednesday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Storm Watch from Thursday afternoon through Friday
evening for Western Plumas County/Lassen Park.

Winter Storm Watch from Thursday afternoon through late Friday
night for West Slope Northern Sierra Nevada.


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