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FXUS66 KSTO 182331

331 PM PST Thu Dec 18 2014

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.


Both Beale and the Davis radars are back up from maintenance
earlier today. We did hear reports of light rain in parts of Shasta
County when the radar was down and current radar imagery does
verify light showers in that region. Otherwise, the rest of our
CWA remains fairly dry. However, one more round of rain and snow
is on its way. A storm offshore is already moving into the far
northern CA coastline and will bring the next notable wave of rain
and snow to interior NorCal on Friday. More widespread
precipitation will move into the Coastal Range late tonight and
then spread into the Central valley and Sierra on Friday. 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

Ridging builds over the Eastern Pacific on Saturday and nudge 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, 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



Mainly VFR conditions across the area this afternoon, except local
MVFR along the west side of the Valley. Next low pressure system
is approaching California, with -RA developing along the Northern
Valley between 09-12z, and Sacramento TAF sites by 15-18z.
MVFR/IFR conditions possible 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



.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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