206
FXUS66 KSTO 110945
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
245 AM PDT Tue Mar 11 2025

.SYNOPSIS...
Dry and seasonable weather prevails again today, with south-
southwest winds becoming breezy throughout the day. A pattern
change toward a prolonged period of active weather is then on tap
from the middle of this week into early next week as a series of
systems affect the region. Periods of moderate to heavy rain and
isolated thunderstorms, heavy snowfall, and gusty winds are
expected to bring major travel impacts to the region at times.

&&

.DISCUSSION...
As split flow aloft prevails across interior NorCal, some
scattered upper level clouds persist early this morning as weather
at the surface stagnates. While south-southwest winds are
expected to increase through the afternoon hours as a robust
trough digs southward from the Gulf of Alaska, another day of
partly to mostly sunny skies should yield one last day of
seasonable temperatures ahead of the active weather. Strongest
winds with the initial push today are expected throughout the
Sacramento Valley and adjacent foothills, with gusts 20 to 30 mph
possible, and some gusts to 35 mph across stronger wind prone
portions of the northern and central Sacramento Valley and
surrounding foothills.

As the aforementioned trough continues to build toward NorCal
Wednesday, a favorable orientation of the associated mid level jet
Wednesday afternoon and evening is expected to bring stronger
gusts of 25 to 35 mph to the Delta, Valley, and foothills from
Interstate 80 southward, with gusts 45 to 55 mph further
northward. Additional gusts to 65 mph will remain possible across
the higher terrain as well. Thunderstorm chances continue to
decrease for Wednesday as instability will likely remain limited
from a lack of daytime surface heating, yet some 5 to 10 percent
probabilities do persist at this time. More appreciable
thunderstorm chances are still expected on Thursday as the trough
centers over the region, introducing some potential for clearing
behind the initial push of precipitation on Wednesday. Current
probabilities of isolated thunderstorm development sit around 20
to 30 percent for the central Sacramento Valley and adjacent
foothills southward on Thursday afternoon and evening. Any
thunderstorms that do develop will be capable of brief heavy rain,
gusty winds, small hail, lightning, and possibly a brief funnel
cloud.

Outside of thunderstorms, heaviest precipitation is expected to
occur on Wednesday, particularly along the Sierra/southern
Cascades. Current probabilities of precipitation exceeding 1.0
inches for most Valley locations outside of the far northern
Sacramento Valley, sit around 15 to 30 percent, jumping to 60 to
80 percent for the foothills and northern Sacramento Valley.
Attendant probabilities of precipitation exceeding 2.0 inches sit
around 70 to 95 percent for locations above 3000 feet.

Snow levels are still expected to vary through the event,
starting around 4500 to 5500 feet at precipitation onset during
the overnight hours into Wednesday, then rapidly falling to 3000
to 4000 feet Wednesday afternoon and evening, before settling
around 2500 to 3500 feet by Thursday. With heaviest precipitation
expected Wednesday afternoon and evening along the Sierra/southern
Cascades, the timing of dropping snow levels will have a
significant bearing on what lower elevation snowfall accumulation
potential looks like. At this time, most accumulations are
expected above 3000 feet across the Coast Range/Shasta County
mountains and above 4000 feet along the Sierra/southern Cascades,
although some nonzero probabilities do exist for accumulating
snowfall as low as 3500 feet. This trend and potential will
continue to be monitored. Forecast snowfall totals from Wednesday
through Thursday remain largely unchanged at this time, with 4 to
12 inches possible above 3000 feet across the Coast Range and
Shasta County mountains and up to 2 feet over peaks, with 1 to 3
feet possible above 4000 feet along the Sierra/southern Cascades
and up to 4 feet over peaks. Probabilities of snowfall rates
exceeding 2 inches per hour still peak around 40 to 70 percent
along the Sierra/southern Cascades Wednesday afternoon and evening
as well.

Precipitation chances from this initial system are then expected
to taper late Thursday into the overnight hours. While this will
lead into a brief reprieve, ensemble guidance is indicating a
shortwave moving through the remnant northwesterly flow pattern on
Friday behind the exiting midweek trough. Very subtle differences
in the timing of this shortwave will have an impact on the
magnitude of lower elevation snowfall potential. Limited time for
snow level recovery is anticipated ahead of this wave, but a swath
of mid level warm air advection is also expected to accompany the
shortwave as it approaches. Ensemble suites only differ on this
feature by about 6 hours, but a slight delay in this warm air
advection could yield some accumulating snowfall into lower
elevations across Shasta County.

The progressive nature of this system will keep most
precipitation confined to Friday, with a rapid drop off in
precipitation chances moving into Saturday. The expected
trajectory of this trough will keep heaviest precipitation totals
across the northern Sacramento Valley and along the
Sierra/southern Cascades, with primarily light showers at most for
much of the Delta, Valley, and foothills. Even still,
probabilities of precipitation exceeding 1.0 inches for Friday
only sit around 40 to 60 percent for the aforementioned heavier
precipitation locations. While some uncertainty in snow levels and
overall snow production continue at this time, additional
mountain travel impacts will be possible to round out the week.
With a prolonged period of active weather expected to encapsulate
much of the next 7 days ahead, be sure to take time now to prepare
for adverse weather impacts, monitor the forecast for additional
updates, and be sure to have a reliable way to receive weather and
travel alerts.

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
Ensemble guidance and cluster analysis indicate an active weather
pattern continuing for interior northern California over the
extended forecast period with another trough building and moving
through the region sometime over the weekend and into early next
week. While some uncertainty remains in exact details with this
storm system regarding timing and strength, additional
precipitation and gusty winds are currently favored. The National
Blend of Models (NBM) currently projects the following
probabilities for this timeframe:

Probability of Rain > 1" Saturday-Tuesday AM: 55-95%
Valley/foothills

Probability of Snow > 24" Saturday-Tuesday AM: 55-95% above 5000`

Probability of Wind Gusts > 40 mph Sunday: 50-80%

Probability of Thunderstorms Sunday-Monday: 5-15%

Latest guidance suggests mostly showery activity on Saturday,
with overall lighter precipitation north of Interstate 80 and over
higher terrain. The more widespread precipitation is currently
favored to move through Sunday into Monday, with lingering showers
over the mountains late Monday into early Tuesday. Cooler than
normal temperatures are also in the forecast, with daytime highs
in the 50s to low 60s in the Valley and lower foothills and in the
30s to 50s in the upper foothills and mountains. Be sure to
monitor the latest forecast at weather.gov/sto and plan ahead for
continued cool, wet and windy weather!

&&

.AVIATION...
VFR conditions expected across interior NorCal today. A storm
system will move through after 06Z Wednesday bringing periods of
MVFR/IFR in the Valley and foothills from rain and MVFR/IFR/LIFR
in the mountains in snow as precipitation spreads inland. Light
winds less than 12 kts expected through 18Z Tuesday, then
southerly winds increase, with gusts up to 25 to 45 kts in the
Valley after 00Z-06Z Wednesday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 11 PM this evening to 11 PM PDT
Thursday for Burney Basin / Eastern Shasta County-Mountains
Southwestern Shasta County to Western Colusa County-Shasta Lake
Area / Northern Shasta County-West Slope Northern Sierra Nevada-
Western Plumas County/Lassen Park.

Wind Advisory from 8 PM this evening to 11 PM PDT Wednesday for
Central Sacramento Valley-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley.

&&

$$