Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 081130
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
330 AM PST Thu Dec 8 2016


.SYNOPSIS...
Wet pattern through the weekend as a series of weather systems
move through northern California. Moderate snow levels expected.
Periods of rain and mountain snow possible for first half of next
week.

&&

.DISCUSSION...
Northern California currently in a showery period between weak
weather systems. Current snow levels over the northern Sierra have
climbed to 5000 feet an continue to rise. Farther north over
Shasta county, trapped cold air has been slow to mix out under
light wind conditions. Airmass supports much higher snow levels so
expect low level colder air to mix out later this morning after
sunrise. Until then, have left up winter weather advisory for
Shasta county mountains. Next weak frontal system now along the
coast will be pushing across the state today reaching the Sierra
by this afternoon. Generally light amounts of precipitation are
expected in the valley with this system but orographics will bring
higher amounts over the Sierra Cascade crest. At this time, snow
levels are expected to rise to mainly above pass levels by later this
morning. Cloudy skies and cool airmass will keep todays highs
below normal. Zonal flow will bring the next Pacific system into
Norcal on Friday keeping the precipitation going. This system
looks similar in strength to todays system with light rain over
the valley and orographics bringing moderate rain to the Sierra
Cascades. Snow levels with this system remain near to a little
above pass levels so impacts to trans Sierra travel should be
minimal. A slightly colder weather system is forecast to move
through the north state Friday night and Saturday. The lower snow
levels could produce more significant travel impacts over the
higher terrain so possibility of winter mountain travel products
will need to be accessed as Saturday grows closer. Sunday could
see the biggest gap in precipitation of the next several days with
models showing norcal in between systems. Moist zonal flow,
however, will keep the threat of showers going through the second
half of the weekend. At any rate, precipitation amounts will
remain light Sunday.
&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)

Low-confidence forecast for NorCal precipitation early next week
as models generally generally build a flat ridge across the area
by Tuesday. EC and GFS operational runs have flipped, and the EC
is now the wetter solution with moisture moving up from the
southwest resulting in widespread precipitation for the area while
the GFS is dry.

Better confidence in another more significant precipitation event
for the region later next week as the ridge is displaced eastward
by a deeper trough showing potential for merging polar and
subtropical flow over the eastern Pacific.
&&

.AVIATION...

Widespread MVFR CIGS/VIS with areas IFR will continue next 24
hours under warm-advection regime. Snow levels gradually rising.
Southeasterly winds 10-15 kts with gusts 20-25 kts in the Central
Valley south of KSAC til about 00Z Friday. Locally strong
southwesterly winds across the higher elevations of the northern
Sierra Nevada.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 AM PST this morning for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Weather Advisory until 10 AM PST this morning for Shasta
Lake Area / Northern Shasta County.

&&

$$



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