Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 192329

329 PM PST Fri Dec 19 2014

Rain and mountain snow this evening as a Pacific cold front moves
through the region. Lingering showers on Saturday for the valley
and through Sunday over the mountains. Dry all areas
Monday/Tuesday under high pressure ridge. Another system may
impact the region Wednesday evening into Christmas Day.


Rain and snow impacted the southern half of our CWA for much of
the day. The main band of precipitation was essentially parallel
to the Interstate 80 corridor this morning and afternoon causing
localized urban and small stream flooding as well as many traffic
issues up in the mountains. Latest radar imagery shows that this main
band is now just south of the I-80 corridor so conditions will
improve for a few hours. However, additional precipitation is
expected generally from the I-80 corridor and southward later
tonight between 6-10 pm. Have kept the Snow Advisory in effect
through 10 pm tonight. Snow levels have been as low as around 5000
ft elevation, but the bulk of snow accumulation is at 6000 ft and above.

The high resolution models show another dose of precipitation
arriving early Saturday morning across the Coastal range into
portions of the valley. Valley rain will taper off from afternoon
into evening (south to north), but the moisture in the Sierra should
keep lingering light snow showers into Sunday. Sierra travelers
should be prepared for continuing light snow through the weekend.

An upper ridge begins to build over the Eastern Pacific on
Saturday and will amplify on Sunday. If skies clear enough early
Sunday morning, then patchy fog development in the valley is
possible. Sunday looks dry over much of the north state but models
continue to show moisture moving over the ridge Sunday afternoon.
Therefore...have kept shower threat over the mountains although
precipitation amounts will be light. Warmer airmass under the
ridge and a little less cloud cover will allow daytime highs on
Sunday to climb to above normal for this time of year. The ridge
strengthens and builds farther inland on Monday which means clear
skies, the redevelopment of patchy morning fog and warmer daytime
highs. JBB

.Extended Discussion (Tuesday through Friday)

High pressure will remain in control for Tuesday into early
Wednesday. Patchy morning fog possible mainly in the Valley each
morning. The main system of interest is still progged to move
through later on Christmas Eve into Christmas Day. Models continue
to be all over the place with solutions with the only agreement
being the appearance of a trough. 12Z ECMWF wettest of solutions
with deep low dropping ESE into So Cal and precip across the entire
area. GEM also depicts closed low into So Cal but results in split
flow to the north and south of local area, leaving us dry. GFS
weakest and furthest north of the bunch with only light precip
brushing far northern portions of the state. Thus, confidence
continues to be low regarding holiday forecast unfortunately. Have
continued with slight to low chance of rain/snow mainly late Weds
morning into Weds night north of I-80 until details are better
resolved. If precip does occur, could cause some travel headaches
across the Sierra as snow levels look to fall to around 4000 feet.
Will continue to highlight uncertainty and will continue to watch
as the holiday week draws near. High pressure will build in behind
this pesky system for Friday into the weekend, resulting in dry




Frontal system is moving through Northern California this
afternoon, with the bulk of precipitation south of I80. Mainly
MVFR with local IFR conditions are accompanying this system in the
Valley, with IFR/LIFR conditions in the mountains. Periodic -SHRA
will continue through tonight and into Saturday. Freezing levels
will be between 5000-6000 ft. SE Valley winds 10-15 kt this
afternoon will decrease to below 10 kt tonight.



.STO Watches/Warnings/Advisories...
winter weather advisory until 10 pm pst this evening above 6000
feet in the west slope northern sierra nevada...western plumas
county/lassen park.


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