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Area forecast discussion 
National Weather Service Sacramento California
318 PM PST Wed Nov 26 2014

Synopsis...
dry and mild weather is expected through Thanksgiving as high
pressure covers the region. Rain is expected to return to the
region by late Friday and continue into early next week. Snow
across the mountains is likely to cause travel difficulties for
the Holiday weekend and into early next week.

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Discussion...
ridge of high pressure over the area today bringing above normal
temperatures and mostly sunny skies. Some high clouds ahead of the
approaching storm system are moving through the area. Temperatures
this afternoon should peak in the mid to upper 60s in the Central
Valley and foothills and 50s and 60s in the mountains which is
around 7 to 15 degrees above normal for this time of year. Mostly
clear skies and remnant low level moisture will bring a return of
the patchy fog to the valleys again Thursday morning. Ridge
weakens Thursday as trough approaches the area but will still be warm
with mostly sunny skies. Temperatures for Thanksgiving afternoon
are expected to be in the mid to upper 60s in the valley and mid
40s to low 60s in the mountains.

The weather will turn cooler and wetter Friday into next week as
several storm systems move through the area. Temperatures start to
cool on Friday as the upper level trough nears the coast. High temperatures
in the upper 50s to mid 60s in the valley and mid 40s to 50s in
the mountains on Friday and drop in the 50s in the valley and 30s
and 40s in the mountains on Saturday. Clouds will increase on
Friday with precipitation expected to start moving into the
coastal range by Friday afternoon. Precipitation will spread
southeast across the area to around the I-80 corridor Friday
evening and farther south into the northern San Joaquin Valley
Saturday morning. Snow levels are expected to be around 7500 ft
Friday and lower to around 6000 feet Saturday. This will bring
snow down to the Sierra passes this weekend possibly causing
travel delays. A few inches of snow are possible in the Sierra
with around 18 inches possible for the top of Mt. Lassen.
Rainfall totals for Friday and Saturday are expected to be around
a quarter to half an inch in the Central Valley and . Generally
around 0.75 to 1.5 inches for the mountains...mainly north of
I-80. Southerly winds will bring breezy conditions on Saturday also.

Extended discussion (sunday through wednesday)

Development of a deep...closed upper-level low off the California coast
during the Holiday weekend promises to bring significant rain/mtn
snow to interior norcal into early next week. A strong probability/
measure of predictability is forecast by the NCEP 15 days 500 mbs
height ensemble for this scenario to unfold. The rmop and the GFS
dprog/dt show a retrogression of the closed low that was to some
extent forecast by earlier runs of the European model (ecmwf). The retrogression of
the upper low has resulted in slower ewd movement and timing of the
precip for norcal. Instead of the heaviest quantitative precipitation forecast expected from sun
nite into Mon...or near the end of the Holiday weekend during the
mass return/exodus of the public...the heaviest qpfs may not occur
until late Mon and/or Tue. This also follows the forecast of the
best period of water vapor (wv) transport into norcal. Thus...the
impacts from the upper low may occur after the Holiday period. (This
does not refer to the impacts from the previous (and relatively
weaker) waves bringing precip to our County Warning Area Fri-sun.)

A high probability of an inch or more of precip is forecast for the
Shasta co area...and siernev for the Sat...sun...Mon periods...with
the highest probabilities in the latter two periods...and a 95%
probability of 2+ inches through Tue. The wpc 7 day quantitative precipitation forecast indicates
about 7-9 inches over the siernev...mainly 1-3 inches for the valley
with the highest amounts in the nrn SAC Vly tapering swd. These
numbers correlate to a likely 95th probability of precip for the
valley and at least "chance" probability for the higher elevations.
Certainly a "dent" can be made in our precip deficit should this
materialize.

Due to the retrogression/slower timing of the models...norcal will
be in the warm air advection zone ahead of the upper low throughout the weekend
with moderately high snow levels. There is a high degree of
uncertainty in the timing and amount of quantitative precipitation forecast Tue/Wed due to the
slower timing of the European model (ecmwf) and the seemingly too progressive GFS.
Thus...later in the efp is subject to a myriad of changes. Jhm

&&

Aviation...

Becoming broken-overcast cirrus tonight and Thu. Patchy early morning
fog/St and local IFR/LIFR conditions in the central Vly and mtn
valleys/basins mainly from 10z-18z Thu.



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Sto watches/warnings/advisories...
none.
&&

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