Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 270617 AAA
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1015 PM PST Fri Dec 26 2014

.Synopsis...
Mainly dry weather will continue for the next few days, with
north winds and frosty overnight lows. Stronger north winds and a
few mountain showers may be possible for early/middle next week.

&&

.Discussion...

Many of the dewpoints in the valley to the N and W of the SAC area
are below freezing and this increases the likelihood of frost over
fog in these locations by Sat morning. From the SAC area Swd to the
Nrn San Joaquin Vly...the dewpoints are above freezing and still
suspect some fog will be possible in this area...especially given
the wet ground. The sites most susceptible for some fog (or a
relatively narrow strip of fog) seem to be MHR...SCK and MOD as the
other sites have been influenced by the dry Nly winds of the last
couple of days...which are now diminishing most areas and will be
light on Sat.

In general... the HR3 shows mainly MVFR vsbys in the valley through
15z...so the lower vsbys Sat morning should be quite local. It will
be a cold nite...but not as cold as what is coming by around Tue/Wed
of next week when energy from the Arctic Circle drops Swd into
Norcal bringing mtn snow showers and the coldest air of the season
at the end of the year (a -3 anomaly over the Nrn Rockys and
portions of the Pac NW depending on the standard pressure chart of
interest.) In fact...it looks like the ol` Polar Vortex will ring
out the Old Year and ring in the New Year over a large portion of
the CONUS.

On Sat...high cloudiness (CI/CS) should spill over the W Coast ridge
and progressively invade the sky. By Sun morning the clouds should
be south of the 80/50 corridor...with clearing across the Nrn
portion of the CWA. Sun looks sunny with near normal max temps.
Winds should pick up on Mon ahead of the energy coming down from the
Arctic Circle.   JHM

A frost advisory has been issued for Saturday morning, with tonight
expected to be the first widespread frost of the season across the
Valley.

Dang

&&


.Extended Discussion (Tuesday through Friday)

The extended forecast continues to look cool with breezy north
winds on Tuesday. There is little potential for precipitation
except for light snow showers up in the Sierra Tuesday.

A cold trough originates from Alaska/northwestern Canada and drops
down through northern California Tuesday. This system deepens and
spreads westward over the area, bringing cold air into the region.
Lower level thickness values bottom out Wednesday and/or Thursday.
Breezy winds are expected on Tuesday into Wednesday, and will
likely reach wind advisory levels with sustained winds of 25 mph
and stronger gusts. The winds should keep the atmosphere mixed in
the Valley and limit frost and colder temperatures.

This system has little moisture to work with, so snowfall amounts
in the Sierra should be light. Snow levels could be low enough to
allow some light snow showers/flurries into the foothills by
Tuesday.

By Wednesday/Thursday, the trough closes off and drops to the
south and east. Winds weaken allowing colder temperatures in the
Valley. The best chance for frost and freezing valley temperatures
will likely be Thursday/Friday mornings when winds subside,
especially on the less windy eastern side of the valley. Highs in
the mountains will remain quite cold through the later half of
the week. The new year should start out dry, with no significant
precipitation events in sight.

&&

.Aviation...

VFR SKC conditions tonight except for isold MVFR vsbys in patchy BR
developing after 12z south of KMYV. Light winds on Sat with cirrus
spreading Swd over TAF sites during the afternoon. Morning frost
expected on aircraft left outdoors until around 18z.

&&

.STO Watches/Warnings/Advisories...
frost advisory from 4 am to 9 am pst saturday carquinez strait
and delta...central sacramento valley...northern sacramento
valley...northern san joaquin valley...southern sacramento
valley.

&&

$$








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