Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 200600
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
955 PM PST Fri Dec 19 2014

.Synopsis...
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.

&&

.Discussion...
Frontal band remnants over the far SErn portion of the CWA will
linger for a few more hours...but generally should be waning.
Extended the WSW til 4 am to account for the snowy conditions from
Hwy 50 Swd. The WAA precip is showing-up on the radars over the S
Bay area ahead of the warm front which will traverse the CWA on SAT
with the gradually building ridge. Normally the ridge would preclude
precip...but the exceeding wet plume over 200 pct of normal along
40N poised to reach the Nrn CA coast...and strong WAA will defy
meteorological science and rain will overspread most of the
CWA...especially N of SAC and over the mtns as well. The WAA will
account for relatively high snow levels...perhaps rising to near or
above the passes Sat evening as the precip finally winds down or
ends.  JHM

Upper ridge 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
weather.

CEO


&&

.Aviation...

Frontal system lingering over the far Srn portion of the CWA where
light precip will continue. Warm frontal rain/showers will begin to
move into Nrn SJ valley after midnight. Next wx system along the Nrn
CA coast will overspread the Nrn portion of the CWA and TAF sites
after 10z or so. Mostly MVFR with local IFR conditions 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.

&&

$$









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