000
FXUS66 KSTO 052147
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
147 PM PST Tue Dec 5 2023


.Synopsis...
The lingering patchy fog in the San Joaquin valley has lifted out
of the area this afternoon, but may reform later again tonight.
Next weather system moves in Wednesday and will bring showers and
mountain snow through Thursday evening, mainly along and north of
Highway 50. Drier conditions on Friday with locally breezy north
winds.

&&

.Discussion...
GOES-18 satellite imagery shows the lingering patchy fog has
dissipated. Some high clouds are moving through the area, with
breaks of sunshine for most of the area. Today will be the last
day of dry weather as an upper-level weather system from the
Pacific Northwest pushing into the region on Wednesday, bringing
rain and snow showers through Thursday night.

Precipitation is expected to begin Wednesday morning starting over
the Coastal Range and northern Sacramento Valley and spreading
across the rest of the region throughout the rest of the day. The
National Blend of Models (NBM) has a 60-95% probability of 1" inch
or more of rainfall from Chico northward on Wednesday. From the
San Joaquin Valley to Sacramento there is a 10-50% chance of
receiving 0.50" inches of rainfall Wednesday. The general
consensus is the further north you are, there will be higher
rainfall totals. Additionally, the NBM has a 10-15% chance of some
thunderstorms to develop, mainly for the northern Sacramento
Valley and the Sierra on Wednesday. Rainfall totals are 0.10" -
0.50" inches from Sacramento to Red Bluff, with higher amounts of
0.75" - 1.50" inches north of Shasta Dam and in the Sierra.
Snowfall is also expected over the Northern Sierra with this
system, with a 10-40% chance of 4" inches or more of snowfall at
pass levels. Snow levels are currently forecast to drop to 6500
feet Wednesday afternoon. A general 2-6 inches of snowfall
accumulation is expected at pass levels Wednesday.

Thursday another weather disturbance pushes into our area, with
lower snow levels, although rainfall totals will be much lighter
than Wednesday totals. Best chances for rainfall are in areas
north of I-80. Areas from Red Bluff northward have a 30-90% chance
of 0.50" inches of rainfall on Thursday with higher probabilities
the further north you go. Generally, 0.20" inches or less of
total rainfall is expected for the central Sacramento Valley. and
areas southward and into the Delta. Latest NBM runs have snow
totals for pass levels have trended up, with and additional 4-8
inches now forecast. Snow levels will be around 4000 feet Thursday
night. With the increased snow amounts and lower snow levels, a
winter weather advisory has been issued for Thursday from 10 am
-10 pm for elevations above 4000 feet in the Sierra Nevada
 Mountains. This will impact traffic on I80 and Highway 50, so
 persons with travel plans should plan accordingly.

Friday the trough will exit the area to our east and upper-level
ridging will develop which will help dry things out. Locally
breezy northerly winds may develop, mainly for the western side of
the Sacramento Valley with northerly wind gusts of 15-20 mph.
Temperatures Wednesday through Friday are expected to cool thanks
to the influence of the upper level trough, with Valley highs in
the mid 50s to low 60s and low 40s to low 50s for higher
elevations.
&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...

Clusters continue to show ridging developing off the coast of
SoCal and extending into the forecast area. Light precipitation
is possible on Saturday and early morning Sunday as a subtle
shortwave in the Pacific NW moves moisture on top and over the
ridge. Chances will be mainly limited the Northern Sacramento
Valley and mountainous areas with low confidence in rain extended
far into the Valley. Chances decrease as you move southward down
the Sierra.

An upper level trough will move into the Great Basin late Monday
and Tuesday, giving the chance for more light precipitation over
the Sierra and breezy conditions. Clusters still indicate
uncertainty on the timing and position of the troughing.

&&

.AVIATION...

One more night of quiet VFR to MVFR conditions for Northern
California before a weather system moves in on Wednesday. There is
still the potential for some IFR/LIFR in the southern
Sacramento/northern San Joaquin airports between 09z-18z. Breezy
south to southwest winds will also impact the northern Sacramento
valley airports ahead of the weather system...mainly from 12z-00z
Thursday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 AM to 10 PM PST Thursday for
elevations above 4000 feet Burney Basin / Eastern Shasta County-
Shasta Lake Area / Northern Shasta County-West Slope Northern
Sierra Nevada- Western Plumas County/Lassen Park.

&&

$$