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Area forecast discussion 
National Weather Service Sacramento California
914 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...(tonight through saturday)
tonight and Thursday morning the dew points are coming up a
little but there should be a lot of high clouds that could help to
prevent a lot of fog from forming. Patchy fog still looks
possible during the late night and early morning hours. For
Thanksgiving the high pressure ridge will begin to break down and
shift eastward.

On Friday some precipitation will be possible over the far
northwestern part of the state in the morning and may spread and
start to precipitate along the coastal range from around Lake
County northward and over northern half of the Sacramento Valley.
There continues to be some timing differences but models do agree
on bringing precipitation to the coastal range and far northern
part of the interior. There is agreement on a jet moving over the
far north so would not be surprised to see some rain start early
during the day on Friday for the northern Sacramento Valley. Snow
levels will be high for the onset of precipitation through Friday
daytime but may lower below major pass trans-Sierra levels Friday
night to impact travel with snow. For Sacramento area and south
the models are pointing towards the start of rain from the evening
hours to late at night or early Saturday morning for the far
southern sections of the County Warning Area.

Saturday will see the rain and higher elevation snow continuing
but below major trans-Sierra pass levels. Major precipitation
discrepancies exist between the models so snowfall could range
from a little more than several inches to a foot or more near the
major trans-Sierra pass levels. Stay tuned for updates and be
prepared to carry chains if traveling in the high country this
weekend.

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

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Aviation...

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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