Weather Service Report


812 
FXUS66 KSTO 211830
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1030 AM PST Sat Jan 21 2017

.Synopsis...
Showers today, then 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)... 
Moist westerly flowcontinues today with scattered showers across
Interior Norcal today...mainly over the mountains. Snow levels 
around 3500 to 4500 feet today and local accumulations of 6 to 12 
inches possible over higher elevations. HRRR showing some 
afternoon CAPE of 200-400 J/Kg and combined with sun breaks and 
steepening lapse rates, will allow potential for isolated 
thunderstorms this afternoon. Breezy southerly winds today but 
speeds expected to remain below advisory criteria...mainly in the 
10 to 20 mph range. Lower 50s for highs forecast in the Central 
Valley today with 30s to 40s for the mountains and foothills.

Upstream, satellite imagery showing next Pacific frontal system
and associated atmospheric river approaching. Blended TPW showing
1 to 1.4 inches along baroclinic zone. Models indicate 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 into wind advisory criteria 
after 06z tonight throughout most of the Sacramento/Northern San 
Joaquin Valley. Southerly wind of 25 to 35 mph with gusts up to 55
mph are expected and could lead to more downed trees and 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. Guidance indicating 
wind speeds drop below advisory criteria Sunday morning with 
fropa, but breezy conditions continue through Sunday evening. 

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)

Extended period of dry weather expected across the region during 
the extended forecast period as models continue to show strong 
ridging along the West Coast. Daytime highs start out slightly
below normal then climb to a little above normal by the end of the
week. Cool nights with fair skies allowing overnight lows to drop
to a little below normal. 

&&

.AVIATION...


Mainly VFR TAF sites today except occasional MVFR/IFR ceilings
with passing showers. IFR ceilings and visibility over Sierra
Cascades. Deteriating conditions after about 03z tonight as next 
frontal system pushes in with widespread MVFR/IFR and lcl LIFR 
conditions by 12z Sunday. South winds 10 to 20 mph today in 
Central Valley increasing after 06z Sunday to sustained up to 30 
knots with gusts to up 50 knots through about 18z Sunday. Isolated
afternoon thunderstorms possible in Central Valley next 24 hours.

&&

.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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Western Regional Climate Center, wrcc@dri.edu