Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 161209

409 AM PST Tue Dec 16 2014

Periods of valley rain and mountain snow through mid-week as
several weather systems move through the area. Brief drying
expected Thursday, then another system is forecast to bring a
return of showers on Friday.


Active weather pattern continues for NorCal the next few days as
large-scale upper trough lingers along the west coast. Several
waves will move through the flow into mid-week bringing periods of
enhanced precipitation to the region.

One wave is lifting off to the east early this morning with
numerous showers continuing over the northern Sierra and isolated-
scattered showers over portions of the Central Valley. However,
any break in showers we see today will be short-lived as another
system arrives later today and tonight spreading more rain and
snow across NorCal along with bringing gusty southerly winds. That
one exits east by early Wednesday, then another moves in later
Wednesday. Following a break Thursday as short-wave ridging moves
overhead, another system is forecast to move in on Friday.

Total additional QPF through mid-week of 1/3-3/4`s of an inch of
rain can be expected in the valley with 1-2 inches in the
foothills and mountains. Snow levels will be moderately low during
the period generally ranging from 3000-4000 feet. 48 hour snow
accumulations of a foot or more will be possible at the higher
elevations with 4-8 inches possible down to around 4000-5000 feet.
This will lead to travel impacts over the mountains with delays
possible at times with chain requirements.


.Extended Discussion (Saturday through Tuesday)...
The Friday system moves through the area, but showers linger over
mountains on Saturday. The GFS, EC, and GEM depict a 590-591 dm
high center over the eastern Pacific Sunday leaving only slight
chances of precip over the Shasta mountains. The high drifts near
the SoCal coast Monday into Tuesday, drying out the region with
significant southern Sac and northern San Joaquin Valley fog
setting up.

GFS and EC flatten the ridge somewhat Tuesday, and the GEM
actually introduces a trough just offshore. Since all models
trended to at least a flattening/weakening of the ridge, we
introduced a slight potential of light rain over Shasta mountains
Tuesday afternoon. JClapp


Scattered showers cont this morning with freezing levels ranging
around 3000-3500 ft MSL in Shasta County to 5000-5500 ft MSL near
I-80/hwy 50. IFR cigs at northern valley TAF sites til near 20z
from -SHRA and/or BR. Another system moves in late this afternoon
and/or early evening for continued periods of precip. JClapp


.STO Watches/Warnings/Advisories...None.


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