206
FXUS66 KSTO 212132
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
132 PM PST Sun Dec 21 2025

For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.


.KEY MESSAGES...

 - Series of atmospheric rivers will bring widespread moderate to
   heavy precipitation today through the holiday week.

 - High snow levels through Tuesday, gradually fall mid week with
   the potential for major holiday travel impacts.

 - Periods of gusty southerly winds through mid week, with the
   strongest today, Wednesday, and Thursday.

&&

.DISCUSSION...

...Today and Monday...

Current satellite shows the long fetch of moisture ahead of the
trough in the eastern Pacific pushing onshore into California.
Strong synoptic lift and moisture feed is aiding in the
increasing coverage of rain across northern California. Radar
shows a swath of rain over the Coastal Range, southern Cascades,
and Sierra which will start to translate down into the valley as
we move through the reminder of today. Rain will be moderate to
heavy at times this evening and overnight. A surge in low level
instability in the northern Sacramento Valley is picked up in
short term guidance. This brings the chance for thunderstorm
activity this afternoon and evening. Chance for higher rainfall
rates up to an inch per hour within Shasta county where rain and
isolated thunderstorms have tended to train over the same
locations.

Along with the rain, we will continue to see strong southerly
winds, with gusts up to 35mph within the southern Sacramento
valley and northern San Joaquin Valley. Areas in the northern
Sacramento Valley toward adjacent foothills and mountains will see
the potential for gusts of 40-55mph this afternoon and evening.
Make sure to secure outdoor belongings and holiday decorations.
Precipitation becomes isolated within the valley late tonight and
into Monday morning before another wave of precipitation moves in
Monday night. Snow levels today and through Monday will be over
7500-8000 feet.

...Tuesday through Saturday...

A brief lull in activity is possible Tuesday morning before we
start to see snow levels drop and precipitation become moderate
to heavy once again. Surging moisture and instability from the
Pacific brings widespread rain, higher elevation snow, and travel
impacts to the area Tuesday through Friday. Snow levels begin to
drop toward 5500 feet late Tuesday and into Wednesday. During this
time, winds will be increasing out of the south once again, with
gusts up to 55mph possible for both Wednesday and into Thursday.
Higher winds combined with heavy snow bring travel impacts within
the mountains during the holiday period. Snowfall 5500-6500 feet
will be up to a foot while areas above 6500 feet will see 3-6 feet
with locally higher amounts at higher elevations.

Rain will be moderate to heavy at times, with flooding in
susceptible urban and low lying areas, including small streams
and creeks. Areas that see thunderstorm activity may see rainfall
rates up to an inch per hour. A flood watch is in effect through
Friday for the flooding potential. Rockslides, mudslides in the
foothills/mountains will be likely. Rainfall will range between
3-8 inches from today through the end of the holiday week for
areas within the Valley, with over 10 inches within potions of the
Sierra north of I-80. If you have travel plans this week plan
ahead, make alternate routes, have backup plans, and carry safety
kits with you in case of an emergency. If you see flooded areas,
turn around don`t drown.

There will be a chance for lingering impacts Friday and into the
early part of the weekend, especially up in the mountains where
high snowfall is likely. Areas in the valley will see improving
conditions, and later the mountains as the synoptic setup aloft
shifts the main track of systems toward the Pacific NW.

&&


.AVIATION...

Areas within the northern Sacramento Valley (RDD, RBL) are
currently in IFR to MVFR ceilings, with rain being reported at
times. Areas around Sacramento points southward are in VFR
ceilings. Ceilings are expected to drop to IVR to MVFR later this
evening and overnight as the rain spreads east and south. Heaviest
rain will be within the Sacramento Valley where visibilities may
drop to 2-3SM with isolated thunderstorm chances. Winds will be
strong out of the south for RDD and RBL, with gusts up to 45kts at
times through the evening hours. Winds should start to drop off
slowly around 06-09z, but remain breezy through the remainder of
the overnight hours and into the end of the TAF period. Areas
around Sacramento and the San Joaquin area will see breezy south
winds through 06z, with gusts up to 30kts. Rain will continue on
Monday, with a brief lull in activity near the end of the TAF
period for the Valley.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday afternoon for Burney Basin / Eastern
Shasta County-Carquinez Strait and Delta-Central Sacramento
Valley-Motherlode-Mountains Southwestern Shasta County to
Western Colusa County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Northern San Joaquin Valley-Shasta
Lake Area / Northern Shasta County-Southern Sacramento Valley-
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

Wind Advisory until 10 PM PST this evening for Central
Sacramento Valley-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley.

Winter Storm Watch from Tuesday evening through Friday morning
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$