Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 201227
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
427 AM PST Sat Dec 20 2014

.Synopsis...
Rain and mountain snow continue today, gradually diminishing
through the day, with some mainly mountain showers lingering into Sunday.
Dry Monday and Tuesday under high pressure ridging. Another
potentially wet system may impact the region Wednesday into
Christmas Day.

&&

.Discussion...
Lingering cold frontal showers exiting eastward this morning while
abundant moisture and warm advection are spreading inland into the
area from a Pacific plume. While dynamics are limited, PW amounts
over an inch will bring additional rain, especially into the
Coastal Range and Shasta County.

Rain and snow continue to be an issue early this morning with a
batch of lingering showers over the Sierra. Sensors show
temperatures on I80 generally in the mid 30s, while webcams show some
rain showers and wet road surfaces. Caltrans reports a mix of
rain and snow over Highway 50 from Twin Bridges eastward with
chain controls in effect. Have continued the Winter Weather
Advisory through 10 am mainly for that area southward with an
additional inch of snow possible keeping roads slippery. Snow
levels will continue to rise through the day with warm advection,
with limited additional accumulation for the afternoon.

High resolution models show precipitation this morning across the
Coastal range into portions of the Valley. Valley rain will taper
off from the afternoon into evening (south to north), but the
moisture in the Sierra should keep lingering light snow showers
into Sunday.

Upper level ridging begins to build over the Eastern Pacific on
Sunday. Enough moisture remains to keep some lingering showers over
the northern mountains and possibly into the northern Sacramento
Valley. Skies over the northern San Joaquin Valley may clear
enough to allow some patchy fog to develop.

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 and Tuesday which means clear skies, the redevelopment of
patchy morning fog and warmer daytime highs. Areas in fog may see
less warming, so temperatures could be tricky in those areas.


.Extended Discussion (Wednesday through Saturday)

Models continue to be all over the place with solutions on the
Christmas Eve system lending poor confidence to the forecast. EC
continues to be the most bullish spreading precipitation southward
into Central CA while both the latest GEM and GFS operational runs
only slightly dent the ridge over the area and spread
precipitation only as far south as the northern mountains. We`ll
continue to monitor trends with this system. Drier northwesterly
flow forecast over the area in the wake of the system heading into
next weekend.

&&

.Aviation...

Widespread IFR/MVFR conditions in -RA/-SN BR will continue as warm
front remains draped across the region. Snow levels 050-060 will
rise to above 080 by early Sunday. Conditions improve gradually by
08Z Sunday.

&&

.STO Watches/Warnings/Advisories...
winter weather advisory until 10 am pst this morning above 6000
feet in the west slope northern sierra nevada.

&&

$$






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