Alta Sierra, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

164
FXUS66 KSTO 182222
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
222 PM PST Thu Dec 18 2025

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

.KEY MESSAGES...

 - A prolonged pattern of wet and unsettled weather is expected
   into next week.

 - Minor impacts are expected through the weekend with periods of
   generally beneficial rain, gusty southerly winds, and high
   snow levels.

 - Colder and wetter storms are likely for the week of Christmas
   bringing travel impacts above 6000 feet.

 - Though exact details remain uncertain this far out, there is
   the potential for major impacts to mountain travel due to heavy
   snow by mid-week (Christmas Eve and Christmas Day).

&&

.DISCUSSION...

...Today Through the Weekend...
More widespread precipitation arrives late tonight into Saturday
as the next system moves across the area. The heaviest
precipitation is expected on Friday, with a possible brief lull
early Saturday morning. Snow show be limited to high peaks with
this relatively warm system. Latest WPC guidance indicates 0.10 to
0.60 inches of precipitation in the Valley, with 0.50 to 2.50
inches in the foothills and mountains. The highest precipitation
amounts are expected over the mountains, generally north of
Highway 50.

The next wave of precipitation arrives late Saturday night into
early next week, bringing widespread moderate to heavy
precipitation and gusty southerly winds. Snow levels are around
8000 feet Saturday and Sunday, so not expecting any travel
impacts. Hi-Res guidance is also suggesting the potential for a
Shasta County convergence zone developing Sunday evening.

Along with the precipitation there will be breezy southerly winds
through the Valley and in the mountains. Gusts up to 35 mph are
anticipated on Friday for areas within the northern Sacramento
Valley, northeast foothills and adjacent mountains. Other than the
precipitation and winds, temperatures will be in the 50s across
the area through the weekend.

...Next Week...

Confidence continues to increase that significant rain and heavy
mountain snow are expected next week with a trough digging into
the eastern Pacific and pumping moisture, instability, and
synoptic forcing into California. This atmospheric river pattern
will bring significant amounts of precipitation. Uncertainties
remain regarding timing, precipitation amounts, and exact track at
this time. Current models show snow levels dropping Monday from
around 8000 feet to 6000-7000 feet, down to 5500-6500 feet Tuesday
and Wednesday. There is a trend towards potential major mountain
holiday travel impacts Wednesday and Christmas Day. Widespread
moderate to heavy rainfall will bring the potential for nuisance
flooding, especially in urban areas. Periods of breezy southerly
winds will accompany the systems; strongest in the Sacramento
Valley, northeast foothills and Sierra. Continue to monitor the
latest forecast as we move into the holiday week and into the New
Year.

&&


.AVIATION...

Ceilings primarily remain IFR/MVFR through the TAF period, though
the southern Sacramento and northern San Joaquin Valleys may see
brief periods of VFR ceilings from 22z today to 8z Friday.
Visibilities lower to MVFR/IFR in the southern Sacramento and
northern San Joaquin Valleys from 05z to 22z Friday. Light
periodic rain in the northern Sacramento Valley and adjacent
terrain through around 12z; then precipitation rates will steadily
increase across interior NorCal with periodic MVFR conditions due
to rain. Southerly to southwesterly winds with sustained speeds
generally 12 kts or less (but gusts up to 25 kts) through 14z.
Sustained speeds increase up to 15 to 20 kts in the northern and
central Sacramento Valley and along mountain peaks after 14z,
gusts up to 30 kts through 00z Saturday.

&&

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

$$