Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 212333
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
333 PM PST Sat Jan 21 2017

.Synopsis...
Next strong Pacific storm impacts Interior NorCal tonight through
early Tuesday with moderate to heavy rain, heavy mountain snow
affecting travel, strong possibly damaging wind, and isolated
thunderstorms. Drier weather later Tuesday through remainder of
next week.

&&

.Discussion (Today through Tuesday)...
Satellite imagery showing next Pacific frontal system and
associated atmospheric river approaching. Blended TPW indicating
1 to 1.4 inches along baroclinic zone. Models suggest widespread
precip spreading into the CWA after about 03z tonight. Strong
cyclogenesis progged off the southern Oregon coast tonight with
10-12 mb NW-SE surface pressure gradient between KMFR-KSAC over
Interior NorCal. Wind speeds increase this evening and become
windy after 06z tonight throughout most of the Sacramento/Northern
San Joaquin Valley. Southerly wind of 25 to 40 mph with gusts 50
to 60 mph. Some isolated spots my reach into lower end high wind
warning criteria. Wind will be strong enough in some areas to
possibly down trees and cause power outages. Moderate to heavy
rain forecast overnight with heavy snow in the mountains. Snow
levels 3000 to 4000 feet overnight.

Front pushes south of the forecast area Sunday morning, then
vertically stacked system off the Oregon coast drops southward
offshore and fills through Monday. This will continue valley
showers and mountain snow. Cold air aloft will steepen lapse rates
and increase potential for thunderstorms Sunday and Monday,
mainly in the afternoon. 500 mb temps of -28 to -32 deg C support
potential for small hail with thunderstorms. Shear profiles show
strong helicity and potential for rotating storms. Guidance
indicating wind speeds decrease Sunday morning with fropa, but
remain breezy through Sunday evening. Snow levels lower Monday
into the 2000 to 3000 ft elevation with some accumulations
possible into the foothills.

Storm total QPF looks to be about 1 to 2 inches in the Central
Valley, 2 to 5 inches in the foothills with 2 to 4 feet of snow
above 4000 feet, locally higher amounts. Decreasing showers
Monday night into Tuesday morning then drier northerly flow
develops as subsidence increase over NorCal.

PCH

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)
Northern California is expected to receive a break in active
weather Wednesday through the end of next week. Model forecasts
are consistent with both the amplitude, timing, and progression of
the upper level flow pattern, which includes two upper level
ridges of high pressure. The first shortwave ridge will develop
Wednesday, but will quickly break down as an upper level trough
passes across the northwestern states. No precipitation is
expected for the forecast area as a result of the passing trough.

Another ridge will build into the west on Friday and for next
weekend, which is anticipated to strengthen and provide dry
weather for all of interior northern California. High/Low
temperatures will be on the cooler side of normal in the long term
period with little cloud cover.

&&

.AVIATION...
Deteriorating conditions after about 03z tonight as next frontal
system pushes in with widespread MVFR/IFR and lcl LIFR conditions.
South winds increasing after 06z Sunday to sustained up to 30
knots with gusts to up 50 knots through about 18z Sunday.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 4 AM PST Monday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Storm Warning from 7 PM this evening to 4 PM PST Sunday
for Mountains Southwestern Shasta County to Northern Lake County-
Shasta Lake Area / Northern Shasta County.

Wind Advisory from 10 PM this evening to 10 AM PST Sunday for
Carquinez Strait and Delta-Central Sacramento Valley-Clear
Lake/Southern Lake County-Motherlode-Mountains Southwestern
Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Shasta Lake Area / Northern Shasta County-
Southern Sacramento Valley.

&&

$$



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