900
FXUS66 KSTO 172229
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
229 PM PST Wed Dec 17 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.

 - Low 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 on Wednesday (Christmas Eve).

&&

.DISCUSSION...

...Today Through the Weekend...

A major pattern change has begun, bringing an extended period of
unsettled weather. The first in a series of waves passed through
overnight into today bringing the first significant precipitation
in a while. This brought up to 2.50" of rainfall amounts in the
mountains, with around an inch over the northern Sacramento
Valley, down to around 0.01-0.05" in the Valley around the I-80
corridor. While precipitation has ended this afternoon, additional
showers are possible again tonight into Thursday, mainly in the
mountains north of I-80. Some patchy morning fog is possible
elsewhere. Overall, there will be a bit of a lull in the active
pattern through the day Thursday. This will brief, as more
widespread precipitation arrives Thursday night, with more
 showers on Friday. Snow show be limited to high peaks with this
relatively warm system.

Further chances for rain and beneficial rain as we move into the
weekend. Chances for moderate to locally heavy rain for areas
along and north of I-80 Saturday into Sunday. There will be a
chance for accumulating snow for the higher mountains, with
probabilities of 4 inches or greater ranging from 25-50 percent
around Lassen and the higher peaks in the Sierra Saturday into
Sunday. Snow levels are around 8000 feet Saturday and Sunday, so
not expecting any travel impacts.

Along with the precipitation there will be the higher winds
through the Valley and in the mountains. Gusts up to 35mph Friday
through Monday for areas within the northern Sacramento Valley
and adjacent mountains. Other than the precipitation and winds,
temperatures will be in the 50s across the area through the
weekend.

...Next Week...

Confidence is improving for a stormy pattern 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 rain.
Uncertainties with the exact timing, development of systems, 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. 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 northern San Joaquin Valley may see brief periods of VFR
ceilings from 22z today to 10z Thursday. Visibilities lower to
MVFR/IFR in the southern Sacramento and northern San Joaquin
Valleys from 06z to 19z Thursday. Brief break in precipitation
today through 03z when light rain will return to the northern
Sacramento Valley. Light, southerly winds generally below 12 kts
through 18z Thursday, increasing afterwards in the northern
Sacramento Valley, the northern foothills, and in the Sierra with
gusts up to 20 kts overnight.

&&

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

$$