Area Forecast Discussion
Issued by NWS Sacramento, CA

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485
FXUS66 KSTO 061749
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
949 AM PST Tue Dec 6 2016

.SYNOPSIS...
Cold overnight temperatures again tonight. A return to wetter
weather is expected Wednesday through Saturday, and again next
week.

&&

.DISCUSSION...
Northwesterly flow continues over Northern California. Yesterday`s
band of upper level clouds has shifted southward, allowing for
optimal radiative cooling conditions across the region.
Temperatures bottomed out near freezing across many Valley
locations. Additionally, dense fog formed along the eastern
portions of the Central Valley, with widespread quarter mile or
less visibilities being reported.

A weak weather system will brush across the region today, and
could bring light snow showers across the northern mountains and
far northern Sierra. The system will additionally reinforce the
cold airmass, bringing perhaps the coldest temperatures of this
extended cold stretch. Widespread subfreezing temperatures are
forecast across the Valley.

A series of more substantial systems arrives starting Wednesday
afternoon/evening. Because of the cold air already in place,
expect snow levels to be rather low when the first system arrives.
In Shasta County, snow levels could be in the 1000-1500 ft range,
and 2500-3000 along the Sierra foothills. Precipitation is
generally expected to be light in those locations. Depending on
location, this cold air will be slow to mix out...but snow levels
will rapidly to 7000+ feet when they do.

Additional impulses arrive Thursday & Friday, possibly into
Saturday. This will come in the form of a narrow plume of
moisture, so some locations may miss out on precipitation with
those impulses. The Sierra will likely see heavy precipitation
with those waves with high snow levels.

&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)


Unsettled pattern looks to continue through much of the extended
period. Model solutions diverge from Friday night with the ECMWF
showing an additional wave of precipitation, perhaps substantial,
during the day Saturday, while GFS remains mostly dry outside a
few Sierra showers. Given such a large difference, have hedged
toward a blend of solutions with precipitation over most of the
area, until solutions are better aligned. Snow levels may drop
lower with this wave should it occur which would further impact
weekend mountain travel.

Next wave moves across the area late Sunday or overnight with a
more subtropical influence. The GFS is much wetter with this wave
vs the drier ECMWF. Regardless, looks like best chance for
widespread precip across the area comes Monday and Tuesday. Snow
levels around 3500 feet across northern mountains and 4500 to 5500
feet in the Sierra on Monday, then increasing into Tuesday with
the warm air advection.   JClapp/CEO


&&

.AVIATION...


Areas of Valley MVFR and local IFR to LIFR in BR/FG again this
morning generally south of MYV. Light northerly flow under 10 kts
thru the period.    JClapp


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from midnight tonight to 9 AM PST Wednesday 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.

&&

$$



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