Area Forecast Discussion
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FXUS66 KSTO 112300

Area Forecast Discussion
National Weather Service Sacramento CA
300 PM PST Tue Dec 11 2018

A weak weather system will brush across far northern California
tonight, otherwise dry weather will continue until the end of the
week when a more active storm pattern returns.


Some light precip forecast across the far Nrn zones overnight as a
short wave trof moves through the Pac NW and across the Nrn/Cntrl
Rockys on Wed. Clouds ahead of this feature are already moving into
Shasta County this afternoon and will overspread much of the CWA
overnite, and may have an inhibiting factor in fog production tonite
by limiting radiational cooling. This feature will be E of our CWA
by Wed morning, and once again NWly flow behind the trof will tend
to "bank-up" the stratus/fog on the E side of the Vly, but it should
also spread Wwd into the Solano County area according to the low
level moisture profile of the KSUU Bufkit. Once the low clouds
dissipate, it should be a sunny day as the higher level clouds pass
through the area as high pressure rebuilds over the region. North
winds will increase in the wake of this system on Wed becoming
locally breezy through portions of the Sacramento Valley. This
should result in a little adiabatic warming over the Nrn Sac Vly for

Dry weather pattern continues on Thu, with a Pacific frontal band
forecast to move into/through Norcal Fri/Fri nite, weakening as it
moves into the Sierra. Reasonable confidence in general around 0.50"
in the Shasta mtns and coastal range with 0.50" to 1.0" over the Srn
Cascade/Sierra north of the 80/50 corridor with amounts tapering
south of Hwy 50. Snow levels AOA 4500-5000 ft will have some
minor travel impacts over the mtn passes then.   JHM



Sat expected to be a mostly dry day, except for some light WAA
precip possible over the Sierra. Generally, Norcal should be
between wx systems on Sat ahead of the long wave trof for Sun/Mon.
The amplitude of this system bodes well for precip, but
confidence is lower in amounts and timing as the longer waves
usually progress slower than progged. Compared to yesterday,
today`s models seem to be about 6-12 hrs slower.

The US W coast AR Landfall tool shows a weak AR (Probability of IVT
>250 kg/m/s) over the Pacific and forecast to reach the coast on
12/16 (Sun) preceded by 2 other ARs. The latter has greater
amplitude, ala the long wave trof, extending from 55N to 35N. There
is actually a little moderate IVT value (>500 kg/m/s) embedded
within the plume between 37N-43N, which is line with at least most
of Norcal and our CWA. The plume is forecast to become parallel to
the coastline and erode/weaken as it moves inland which doesn`t bode
well for significant precip E of Sierra, but will at least result in
a wetter storm for Norcal then its predecessor on Fri. The lack of
duration over our CWA and lack of an orthogonal trajectory to the
Sierra will keep precip amounts lower than a more favorable
trajectory and orientation. Very early, preliminary estimates of
liquid precip for the Sun-Mon storm suggests 2-3 inches over Shasta
County, and 1-2 inches over coastal range and the Sierra especially
north of the 80/50 corridor, and over an inch in the Nrn Sac Vly
tapering to two-thirds to three-quarters of an inch over the rest of
the Vly. This system should cause greater snow impacts over the
Sierra Passes than the Fri system with snow levels down to around
5000-5500 kft. Daytime temperatures will remain near or a little
below normal throughout the extended period with occasional breezy
southerly winds as weather systems move through the area.

A strong upper level ridge building into Norcal will bring an end
to most of the precip and a return to strong subsidence and Vly
stratus/fog on Tue.  JHM



VFR conditions are expected through the evening, with fog
formation expected once more in the Valley. IFR to LIFR conditions
possible south of Marysville. Winds will be light and variable
overnight before southward winds in the Valley increase tomorrow
afternoon to 15 knots, with gusts up to 25 knots.




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