Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 281605
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
905 AM PDT FRI AUG 28 2015

.SYNOPSIS...
Pacific storm approaches today and moves through late tonight and
Saturday bringing cooler temperatures and some precipitation...
mainly north of Interstate 80. Dry Sunday through next week with
below normal temperatures.


&&

.DISCUSSION...
Pacific frontal system is approaching the West Coast and will bring
some precipitation to Interior Northern California late tonight and
Saturday. Satellite imagery showing baroclinic leaf approaching 130W
and blended TPW revealing PWS in excess of 1.5 inches along the
front. System will progress today spreading increasing clouds over
the CWA generally AOA 500 mb, which will help to lower high
temperatures this afternoon to mainly upper 90s for the Central
Valley.

As system progress, it will become entrained into flow associated
with higher latitude short wave tonight. Surface low deepens and
lifts NE overnight while upper level support weakens. Precip begins
spreading into NW portions of Interior NorCal after midnight.
Southern portions of frontal system move through Saturday but
baroclinic zone and integrated water vapor transport weaken as main
dynamics lift NE through the PacNW. As a result, model QPFs are
light with precip generally north of I-80 and greatest amounts
(around a third of an inch or less) over the Coastal Range and
Western Shasta mountains. Breezy southerly wind develops tonight
over the northern half of Interior NorCal, peaking near low end wind
advisory Saturday morning as front moves through. Synoptic cooling
and cloudiness will result in high temperatures Saturday upwards of
10 to 15 degrees below today. Highs expected in the lower to mid 80s
for the Central Valley with mainly 50s to 70s for the mountains and
foothills.

Long wave trough remains along 130W Sunday into next week with
embedded weak vort maxes moving through, mainly north of the
forecast area. Temperatures rebound slightly Monday but onshore flow
and broad troughing aloft keep highs below normal through Friday.

PCH

.EXTENDED DISCUSSION (Tuesday through Friday)

A broad trough pattern will persist over NorCal through the
extended forecast. In general, interior NorCal will experience
cooler than average weather, but there is currently low confidence
that any rain will impact our region. Daytime highs from Tuesday
through Friday will range 2-12 degrees below normal. It looks
like Wednesday and Thursday will be the coolest days: valley highs
will be in upper 70s to upper 80s and mountain highs will range
about 60-80 degrees.

The trough appears to deepen southward towards the end of the week
and the ECMWF hints at some precipitation working its way into
portions of NorCal on Friday, but the GFS stays dry. With low
confidence in rain, have kept the forecast dry for the extended
period.  JBB


&&

.AVIATION...

Pac fntl sys apchs tda then movs thru Intr NorCal late tngt thru
Sat. VFR conds excp lcl MVFR/IFR conds poss mnly N of I-80 and omtns
in pcpn with fntl sys btwn 06z Sat and 00z Sun. Sly sfc wnds incrsg
in Cntrl Vly this aftn into eve with lcl gsts up to 35 kts poss N of
I-80 btwn 06z-15z Sat. Lcl SWly sfc wnd gsts 40-50 kts poss ovr hyr
mtn trrn, mnly N of I-80 tngt aft 06z thru midday Sat.


&&

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

$$



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