413
FXUS66 KSTO 312109
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
109 PM PST Wed Dec 31 2025
For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.
.KEY MESSAGES...
- Moderate travel impacts Friday through Monday, from heavy
mountain snow and wind. Minor travel impacts for the foothills
and valley.
- Unsettled weather pattern continues into next week.
&&
.DISCUSSION...
...Today and New Years Day...
The first wave of energy from an upper level system off the coast
of CA is continuing to move north and east through the state this
afternoon and evening. This brings precipitation chances to the
region, with snow levels over 8500 feet. Precipitation will become
scattered to widespread across the area, with forecasted amounts
between 1 to 3 inches from today through tomorrow night. Highest
amounts at higher elevations. Rain becomes isolated in coverage in
the Valley, with continued widespread chances up in the mountains
late Thursday and into Friday morning. Snow levels will start to
decrease as we move into Thursday, with levels reaching 6500-7000
feet by Thursday afternoon and evening as colder air is wrapped
around the system into CA. Temperatures will be in the 50s on
Thursday within the Valley, and 40s at higher elevations.
...Friday through Monday...
The main synoptic level system over the Pacific moves toward the
coast on Friday bringing sufficient moisture and instability
toward the region. Precipitation overspreads the region Friday
through the weekend and continuing into the early part of next
week. Moderate to possible heavy rainfall at times, with rain
rates up to a half in per hour possible. Forecasted rainfall will
range between 1 to 3 inches, with the highest in the foothills.
Locally higher amounts can`t be ruled out if any area experiences
training thunderstorm chances. These chances are low at this time.
Thunderstorm chances increase Saturday and into Sunday morning as
an instability axis sets up along the coast and into the Valley.
MUCAPE reaches 500 J/kg, with sufficient moisture transport, and
low level shear. A stray stronger storm can`t be ruled out
Saturday afternoon/evening and again Sunday morning. This is where
the potential exists for rainfall rates reaching a half in per
hour around thunderstorms. Rain will continue into Sunday
afternoon/evening and again early next week.
As the system moves onshore, colder air will push down from the
north helping drop snow levels. Friday into Saturday snow levels,
remain around 6500-7500 feet and drop off toward 5000-6000 feet
late Saturday and into Sunday. Latest guidance wants to push out
the colder air moving down from the north toward Sunday and into
Monday, which would cut into some of the snow totals.
Accumulations are uncertain at this time but may range from 2 to 4
feet above 5000 feet. Locally higher amounts are possible at
higher elevations. Winds could gust as high as 45 mph and cause
dangerous travel conditions when combined with the heavy snow. If
you plan to travel this week and into the weekend, make sure you
have alternate routes, backup plans, and carry a safety kit with
you at all times.
Long range guidance looks to continue the feed of moisture and
instability into the region mid next week bringing further
precipitation, mountain snow, and breezy conditions.
&&
.AVIATION...
Visibilities improved today, with a few MVFR conditions lasting
through this afternoon. Ceilings have increased, with a few
locations near MVFR otherwise VFR. Rain will move in from the
south this afternoon and evening becoming widespread later this
evening and overnight. Ceilings drop to IFR/MVFR, with visibility
reductions. Rain continues overnight and throughout tomorrow,
with IFR/MVFR conditions.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday afternoon through Sunday morning
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.
&&
$$
