National Weather Service Text Product Display

Area Forecast Discussion
Issued by NWS Sacramento, CA
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FXUS66 KSTO 010500
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
900 PM PST Tue Jan 31 2017

.Synopsis...
Dry with patchy morning valley fog through Wednesday. Wet pattern
returns Wednesday night with heavier rain and mountain snow on
Thursday and Friday. The wet pattern may continue into next week.

&&

.Discussion...
High clouds are moving over the area this evening. Dewpoints are
up this evening but a better presence of high clouds tonight will
help to keep fog development patchy. Any breaks in the cloud layer
could lead to some rapid development of fog. A few sprinkles may
occur during the afternoon ahead of the main band which is still
on track to move into the area late Wednesday night and Thursday
morning. Current forecast is still on track so no changes.

.Previous Discussion (Tonight through Saturday)... Little overall
change is expected through Wednesday with patchy morning fog,
cool mornings, and mild afternoon temperatures continuing.

An approaching upper low and associated frontal system in the
eastern Pacific will bring a return of wet weather to NorCal
starting Wednesday night and continuing into the weekend. By
Friday, an inch or two rain will be possible in the valley with
1-2 feet of snow in the mountains above 6K ft; local amounts of 3
to 5 ft or more possible over the peaks. Gusty southerly winds
will also develop across the region on Thursday and again Friday.
A the winter storm watch has been upgraded to a warning for the
mountains valid for Wed night into Friday night. The wet pattern
may continue into Saturday, but taper off a bit, especially in the
Valley.    JClapp

&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)


Unsettled pattern will continue across interior NorCal during the
extended period. Precipitation chances diminish Saturday night
into early Sunday as model guidance is less robust in building
ridging into the area briefly on Sunday. Lingering shower activity
will remain mainly over higher terrain.

Pattern becomes more active as an upper trough drops southward
and deepens along the West Coast. However, there is some model
uncertainty in terms of timing and evolution of this upper system.
The ECMWF absorbs an EPAC low pressure system while the GFS
remains out of phase. Regardless, upper system should move through
Sunday night into Monday with widespread precipitation and
another round of gusty winds. Snow levels will remain in the
5000-6000 feet range as the bulk of the precipitation moves
through. Cold air aloft will follow behind the frontal system with
potentially lower snow levels. Temperatures are expected to be
below average by the end of the forecast period.

&&

.AVIATION...

General VFR conditions across TAF sites the next 24 hours. Brief
period of MVFR to IRF conditions from KSMF southward Wednesday
morning. Increased high cloud cover should limit widespread fog
formation.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 10 PM Wednesday to 4 AM PST Saturday
for Mountains Southwestern Shasta County to Northern Lake County-
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

Wind Advisory from 4 AM to 10 PM PST Thursday for Carquinez
Strait and Delta-Central Sacramento Valley-Clear Lake/Southern
Lake County-Motherlode-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&

$$
National Weather Service Regional Headquarters
