Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 081852
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1052 AM PST Thu Dec 8 2016


.SYNOPSIS...
Wet pattern through the weekend as a series of weather systems
move through northern California. Periods of rain and mountain
snow possible into early next week.

&&

.DISCUSSION...
Snow levels have risen significantly and road conditions in Shasta
County and over the Sierra have improved so this morning`s Winter
Storm Advisory for snow has been allowed to expire.

Main focus for today will be looking at snow potential Friday into
early Sunday. Latest CA-NV River Forecast Center precipitation
forecasts have increased amounts during this period. Snow levels
would generally be around 6000 ft or higher so snow impacts would be
limited to the higher elevations over the Sierra. Once
coordination is complete with neighboring offices, we`ll decide if
any Advisories or Watches need to be issued with this afternoon`s
forecast package for snow. JBB

Previous Discussion...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.

&&

&&

$$


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