Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 171717
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
339 AM PDT Tue Oct 17 2017

.SYNOPSIS...
Dry weather thru mid-week. Rain chances along with high mountain
snow and cooler temperatures late in the week followed by a
warming trend this weekend into early next week.

&&

.DISCUSSION...
Seeing some more high cloudiness move into Norcal as our area is in
between 2 wx systems, one to the NW and the other to the SSW. Clouds
across the N are associated with a weakening front moving into the
Pac NW, while the clouds to the south are from the subtropical flow
associated with the short wave lifting NEwd from the vicinity of
28N/125W. Some of this moisture appears to be the remnants from the
decaying low pressure system off the Baja Coast, and is quite moist
and unstable with hundreds of C-G strikes. This moisture gets
shunted SE of our CWA by the WNW flow developing over Norcal as a
progressive short wave moves across the Pac NW today.

Low pressure system over the Wrn Aleutians is forecast to deepen a
trof over the NErn Pac and into the Wrn States Thu/Fri. This will
drive a frontal band across Norcal mainly Thu nite/Fri morning.
NAEFS anomaly table returns a modest +1 anomaly to the coast Thu
evening, and spreads it Ewd into the Sierra by 12z Fri, followed by
lowering PW and a drying air mass. Thus, most of the rain in our CWA
should fall Thu nite into Fri morning.

Prefer a blend of the ECMWF/GFS over the Nrn mtns as the ECMWF is
much wetter than the GFS, and prefer the GFS over the Sierra, as the
ECMWF has been trending lower on the QPF than the GFS. The WSWly
flow with the approaching trof/frontal band should provide a
favorable orographic trajectory for the Sierra Thu nite and Fri
morning. Colder air behind the frontal band expected to lower snow
levels below the major passes on I-80/US-50 where an inch or two of
snow could accumulate. Wetter mountain areas may see as much as an
inch of liquid precip while the valley will generally see less than
a quarter inch and most locales probably just a few hundredths.  JHM

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
The upper trough pushes east and weakens Friday night into
Saturday morning making way for drier and warmer weather over the
weekend. Daytime highs in the Valley will warm into the upper 70s
and low 80s by Sunday. For the foothills and mountains, Sunday
highs will rise to the 60s to mid 70s. Dry weather with additional
warming for the beginning of next week. JBB

&&

.AVIATION...
VFR conditions with light winds. Valley winds at TAF sites will
be less than 10 kts. Winds over higher terrain will be light with
a diurnal pattern.

&&

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

&&

$$



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