000
FXUS66 KSTO 202243
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
243 PM PST Mon Jan 20 2020


.Synopsis...
Widespread precipitation chances return Tuesday and Tuesday night
night with a few inches of snow possible at pass level. Dry
conditions return for the end of the week, then another storm is
possible by late weekend.

&&

.Discussion...
Disturbance passing over central California is keeping clouds over
the area this afternoon, but no precipitation. Skies will remain
mostly cloudy through the evening. The next system will pass
through Tuesday with light valley showers and mountain snow. The
heaviest rainfall will be over the southern Cascade Range
including the Redding area where 0.50 to 1.00 inches will be
possible. Less than 0.25 of rain is expected over the southern
Sacramento Valley southward. This system will be warmer than last
weeks storm with snow level generally above 5000 feet. Expect 3
to 5 inches of snow above 5000 feet over Interstate 80 with the
best chances Tuesday afternoon. Higher Sierra peaks could see up
to 8 inches. The higher snow levels and low snowfall rates should
decrease travel impacts, although still could see chain controls.
Dry and warmer conditions Wednesday through Friday, as upper
ridge builds in from the Pacific.

&&
.EXTENDED DISCUSSION (Friday THROUGH Monday)...
A low-amplitude shortwave will cross the Oregon/California border
early Friday keeping a few showers around over Shasta County. In
its wake, heights gradually build with broad southwesterly flow
aloft prevailing through the first half of Saturday. Then the
focus shifts toward the next system which may be a bit more
impactful. While the guidance continues to struggle with the
timing and magnitude of the approaching shortwave, there is
agreement upon the return of wet weather late Saturday into
Sunday. ECMWF ensemble probabilities exhibit higher values than
the GEFS members so some ensemble spread remains. The current
thinking suggest decent rainfall amounts over the Valley,
foothills, and Delta with moderate snowfall accumulations across
the Sierra-Cascade range, generally around pass level and above.
It is too early to suggest concrete amounts, but do expect some
mountain travel impacts. Thus, it continues to bear watching as
models iron out their differences. Residual shower activity to
linger into Monday morning before an upstream ridge moves in to
start next week. ~BRO

&&

.AVIATION...
A Pacific system will spread rain and mountain snow after 06Z
Tuesday; mainly MVFR/IFR conditions are expected in the Valley
with IFR/LIFR over the mountains. Initial winds are expected to be
around 5 knots or less, while south winds will increase after 10Z
Tuesday. Conditions become locally breezy in the afternoon over
the northern Sacramento Valley with gusts up to 20 to 30 knots at
times.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$