Area Forecast Discussion
Issued by NWS Sacramento, CA

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998
FXUS66 KSTO 101218
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
418 AM PST Sat Dec 10 2016


.SYNOPSIS...
Wet weather tonight through Saturday. Periods of wet weather
likely to continue next week, with significant mountain snow
possible Tuesday.

&&

.DISCUSSION...

A very moist plume of Pacific moisture is bringing widespread
precipitation to the area. The most favorable area for
precipitation is over the northern Sierra, where rates of around a
half inch an hour are expected this morning and into the
afternoon. This could bring totals of around 4 inches there by
early evening, with around 1 to 3 inches in the foothills, and the
Valley seeing around an additional half inch today. Valley
precipitation will wind down this evening as the moisture plume
shifts southward and drier air moves in.

Snow levels with this warm event are quite high this morning,
over 9000 feet. This will keep snow accumulation from being an
issue except over high peaks today. Pass levels could see some
accumulating snow this evening as snow levels drop, but
precipitation will be winding down at that point. There could be a
few inches of snow at locations such as Donner Pass on I80 and
Echo Summit on Highway 50.

Breezy southerly winds this afternoon in the Valley could gust
to 35 mph this morning, then will decrease in the afternoon. Wind
Advisory level winds could briefly be reached in a few isolated
spots mid morning. The Sierra could also see ridge winds gusting
to around 45-50 mph today.

Mainly dry weather is expected Sunday into Monday as a flat ridge
of high pressure moves across California. Moist flow to the north
will bring a slight chance of light precipitation to northern
Shasta County.

Models have been inconsistent with the next system on Tuesday, but
are starting to trend together better towards an increasingly
wet event. A moist plume coupled with cool air could bring
significant snow to the Sierra-Cascade range. Have bumped up snow
amounts to around a foot over the northern Sierra. This would
cause significant travel problems if it comes together as
currently projected, especially Tuesday afternoon and early
evening. EK

&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)


Moisture tap from the subtropics into northern California
continues into the extended period. GFS and ECMWF both showing
precipitation over the entire CWA on Wednesday. Slight ridging
over the southwest U.S. should bring moderately high snow levels.
Upper shortwave trough dropping into norcal on Thursday will keep
precipitation going on Thursday. Moderate precipitation will be
possible over the higher elevations where orographics play a role.
Models show main upper trough digging into the Great Basin on
Friday bringing northerly flow aloft to the north state. This
northerly flow should bring drying but norcal remains under
cyclonic flow so some light precipitation may be possible in moist
airmass. At this time, all extended models bring drying next
Saturday. Have therefore kept end of extended period dry with
clearer skies but cool northerly flow will keep daytime high
temperatures below normal.

&&

.AVIATION...

Widespread MVFR/IFR continue next 18 TO 24 hours as Pacific
frontal band slowly moves southeast across norcal. Some
improvement behind front over central valley after about 06z.
Gusty southerly winds over the central Valley through about 18z
with gusts to 25 to 30 knots.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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