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Area forecast discussion 
National Weather Service Sacramento California
341 PM PST Wed Dec 17 2014

Synopsis...
yet another wave of rain/snow moving in tonight. A brief break in
precipitation some areas on Thursday. Next frontal passage on
Friday with light to moderate rain and higher elevation snow into
Saturday morning. Mountain showers possible over the weekend but mainly
dry in the valley. Dry all areas Monday through mid week under
West Coast high pressure ridge.

&&

Discussion...
showers have lingered along the western Sierra slopes for much of
the day. Radar shows the next round of moisture already impacting
the central and northern California coastal counties. This next wave of
precipitation will move eastward this evening. High resolution
forecast models all in fairly good agreement that rain will start
impacting the Central Valley after 5 PM with rain moving into the
Sacramento Metro region around 7 PM. This moisture will continue
eastward into the Sierra and snow levels will remain around
4000-4500 ft. Thus, we extended the Winter Weather Advisory for
snow along the western Sierra slopes through 4 am Thursday.

Precipitation will taper off on Thursday bringing interior norcal
a brief, but drier respite of weather. However, patchy fog with
some areas locally dense, could develop in portions of the valley
due to lingering moist air and the cold early morning
temperatures. The dry pattern will be short-lived. It sounds
repetitive, but, once again...another round of rain/snow will
impact norcal starting late Thursday night through all of Friday
and into Saturday morning. Snow levels will be higher with this
system at around 5000-6000 ft. The northern Sacramento Valley
(redding-Red Bluff vicinity) and higher terrain will get the bulk
of precipitation. Around a third of an inch to half inch for the
northern Sacramento Valley and a half inch up to an inch in higher
terrain. The rest of the valley will generally range from about a
tenth of an inch up to a third.

Upper ridging begins to rebuild on Saturday with more
amplification on Sunday. As a result...should see a shift in the
precipitation threat to the north with Sunday expected to remain
dry all areas with the exception of the far northern mountains
over Shasta County.



Extended discussion (sunday through wednesday)

Medium range models similar in transitioning to a drier weather
pattern over the weekend into early next week. Some light precip
continues to be depicted over the Shasta mountains Sunday,
otherwise dry weather with the main weather concern being impact
of valley stratus and/or fog nights and mornings. Models
strengthen upper high in epac with associated upper ridge building
over interior norcal.

Longer range models are struggling with the evolution of a
deepening trough over the Pacific northwest toward the middle of
next week. The European model (ecmwf) and parallel-GFS offer a solution that brings
the system farther westward, which could bring some low elevation
snow to the Sierra. The lo-res GFS and Gem swing the trough through
The Rockies, which would be a drier solution for northern
California. For now, we've included "chance" wording in the
forecast focusing on the Sierra.

Dang / jclapp



&&

Aviation...

Trof movg east this mrng flwd by 2nd trof this aftn into tngt then
upr rdg Thu. For intr norcal, areas MVFR/IFR tda into Thu mrng in
prec with LCL LIFR omtns. Sn lvls 040-045 ft amsl.



&&

Sto watches/warnings/advisories...
Winter Weather Advisory until 4 am PST Thursday above 4000 feet
in the West Slope northern Sierra Nevada...western Plumas
County/Lassen park.

&&

$$

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