Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 190537
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
935 PM PST Thu Dec 18 2014

.Synopsis...
Fairly dry today for the region. Next frontal system moves through
NORCAL Friday bringing rain and mountain snow. Drying south on
Saturday with a few showers north especially over the mountains.
All areas dry on Sunday except far northern Shasta county
mountains. Dry Monday/Tuesday under high pressure ridge. Slight
chance of mainly mountain showers on Wednesday.

&&

.Discussion...
Main short wave energy with the incoming trof is N of 40N and moving
towards/into the Pac NW brushing by N of the CA/OR border on Fri.
Just to the S...and along 130W...weaker short wave energy is
enhancing a small area of moisture behind a well defined frontal
band now moving inland with the leading edge near the Wrn Shasta Co
border. This frontal band should zip across Norcal tonite...with
another area of enhanced moisture moving inland during the day on
Fri.

Light rain has been lingering over Wrn Shasta Co this afternoon and
will soon be overrun by the frontal band by around midnite. Rainfall
rates should increase there with the frontal band moving into the
Siernev mainly after 12z...as well as the SAC-SCK areas.   JHM


.Previous Discussion...

The forecast shows valley rain totals ranging 0.10" to 0.50" with
the higher amounts in the Redding and Red Bluff vicinity. The
Sacramento Metro region should get around a quarter of an inch and
areas southward will be closer to a tenth. Primary concern with this
system is snow impacting travel along the Sierra on Friday. Have
issued a Winter Storm Advisory for snow above 6000 ft along the
Western Sierra slopes from Friday 4 am to 10 pm. Sierra traffic
tends to be heavier on Fridays and we`re expecting 3-6 inches of
snow near pass levels which will likely cause traffic delays and
chain restrictions. Mountain snow showers are expected to linger
into Saturday, but any additional snow accumulation will be light.

Ridging builds over the Eastern Pacific on Saturday and nudges into
the west coast late Sat/early Sun. Lingering showers may continue
to slide over the top of the ridge and impact far NorCal through the
weekend due to strong WAA, otherwise, most of our CWA will be dry.
Clearer skies and a warming airmass under the ridge will allow
daytime highs to warm to near normal on Saturday and to a few to
several degrees above normal on Sunday. JBB


.Extended Discussion (Monday through Thursday)

Main concern in long term is around potential system for Christmas
Eve/Christmas Day.

Dry weather will continue Monday into early Wednesday as high
pressure ridge remains in control across the region. Daytime temps
will max out around 60 in the valley and upper 40s to 50s in the
foothill/mountains. Only impact in this period will be areas of
valley fog each morning with lingering surface moisture. High
confidence for this period and it will lead to a few good travel
days.

The next system of interest is progged to move through late
Christmas Eve into Christmas Day as it drops SE from the Pac NW into
the Great Basin. Model solutions continue to be all over the place
as previously advertised. 12Z run of the ECMWF...which was the
strongest and wettest of the bunch and mirrored the latest GEM and
parallel 13km GFS...has flip flopped from previous run and now
mirrors the weaker, more progressive GFS solution. This would lead
to a mainly dry holiday period, especially in most locations in
the Valley. Of bigger note would be infiltration of colder air and
lower snow levels. Snow levels could drop to 3000-3500 feet by
Thursday with accumulating snow and travel headaches likely if
a stronger system does materialize. Overnight temps late in the week
could also drop into the 30s in some spots in the valley leading
to frost. Confidence is low in details and chances for
precipitation at this point so have not made major changes to the
going forecast. Will need to be monitored as we get closer. CEO

&&

.Aviation...

Next low pressure system approaching California, with -RA developing
along the Northern Valley between 09-12z, and Sacramento TAF sites
by 15-18z. MVFR/IFR conditions in the Valley, with IFR/LIFR
conditions in the mountains. Snow levels will be between 5000-6000
ft. Southeast winds will increase to 10-18 kt late tonight into
Friday.

&&

.STO Watches/Warnings/Advisories...
winter weather advisory from 4 am to 10 pm pst friday above 6000
feet in the west slope northern sierra nevada...western plumas
county/lassen park.

&&

$$





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