863
FXUS66 KSTO 130903
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
203 AM PDT Thu Mar 13 2025
.SYNOPSIS...
Active weather continues through the end of the week, with a
brief early weekend lull followed by another system late Sunday
into Monday. Some low elevation snowfall possible Friday morning.
Periods of moderate to occasional major travel impacts expected.
&&
.DISCUSSION...
Scattered convective precipitation lingers across interior NorCal
early this morning as mostly cloudy skies and breezy winds
prevail. Primary impacts from any stronger showers will be
occasional heavier precipitation rates, although some low chances
for isolated thunderstorms will persist through the morning as
remnant instability persists. While some small hail cannot be
completely ruled out this morning, threats from this elevated
convection will be mostly tied to brief heavy rainfall, gusty
winds, and lightning. Instability is then expected to increase
this afternoon as low elevation clearing builds in behind morning
precipitation. Some 25 to 35 percent probabilities of thunderstorm
development then exist this afternoon, with highest probabilities
across eastern portions of the Valley into the foothills. Overall
precipitation totals through the remainder of the day will be
largely tied to this scattered activity, with generally 0.1 to
0.25 inches of precipitation expected at lower elevations and
higher totals of 0.5 to 1.5 inches across higher elevations.
Snow levels are expected to remain relatively steady around 2500
to 3500 feet today, with the majority of accumulating snowfall
remaining above 3000 feet through this evening. While heaviest
snowfall has generally concluded, periodic times of snowfall rates
up to 1.5 inches per hour will be possible throughout the day
with any stronger convective cells aided by orographic lift moving
along the terrain. Additional snowfall totals of 8 to 12 inches
will be possible above 4000 feet along the Sierra/southern
Cascades through this evening, with some 30 to 60 percent
probabilities of snowfall greater than 12 inches above 5000 feet.
Very little downtime in mountain precipitation impacts is
expected between the exiting system and a rapidly arriving system
overnight into Friday. Details around snow levels remain uncertain
but nonzero probabilities of accumulating snowfall as low as 1000
feet in the northern Sacramento Valley and as low as 1500 feet
along the Sierra/southern Cascades foothills do exist,
particularly early Friday morning. Despite the quick moving nature
of this system, periods of moderate to locally heavy snowfall
will be possible at times on Friday. For the Sierra/southern
Cascades, probabilities of exceeding 8 inches of snowfall on
Friday sit around 40 to 80 percent above 4000 feet. Across the
Coast Range/northern Sacramento Valley, probabilities of exceeding
8 inches of snowfall on Friday sit around 40 to 80 percent above
2000 feet. As a result, additional travel impacts are expected
along the Sierra/southern Cascades and along portions of the
Interstate 5 corridor as well.
While the orientation of the passing shortwave on Friday will
keep precipitation totals for much of the Valley under 0.25
inches, a period of gusty southerly winds is expected from mid
morning through the afternoon. Current probabilities of wind gusts
exceeding 40 mph on Friday sit around 40 to 70 percent across
most of the Valley on Friday. As the shortwave remains
progressive, a brief period of ridging aloft looks to build in
through most of the weekend. Some showers may linger across far
northern Shasta County during this time, but predominantly dry
weather is anticipated for the remainder of interior NorCal,
although temperatures will remain near to slightly below normal.
&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Some uncertainty continues with the next expected trough late
weekend into early next week, but additional periods of at least
moderate precipitation are anticipated as it moves through.
Ensemble guidance generally agrees that the overall trajectory of
the system would favor potential for slightly higher precipitation
totals relative to the Friday system, but some uncertainty
regarding the magnitude of the attendant atmospheric river plume
keeps forecast confidence in exact details low at this time.
Current probabilities moving into next week are as follows:
Probability of Rain > 1" Late Sunday-Tuesday AM: 20-40% Valley/foothills
Probability of Snow > 12" Late Sunday-Tuesday AM: 60-95% above 4000`
Probability of Wind Gusts > 40 mph Sunday: 60-95%
Probability of Thunderstorms Monday: 15-25%
It continues to look like most precipitation is expected to be
coming to an end by Tuesday morning, with primarily lingering
mountain showers anticipated at this time. Ensemble guidance is
trending toward continued active weather moving past the extended
forecast period, but consensus indicates a stretch of dry weather
much of Tuesday through Wednesday. Regardless, be sure to monitor
the latest forecast at weather.gov/sto and plan ahead for
continued cool, wet and windy weather into early next week!
&&
.AVIATION...
Predominantly VFR conditions expected at TAF sites next 24 hours,
although occasional MVFR/IFR possible in isolated -SHRA or -TSRA
through 22z. IFR/LIFR expected next 24 hours along Sierra. South
to west winds generally less than 12 kts expected, although some
gusts to 20 kts possible through the Delta, southern Sacramento
Valley, and northern San Joaquin Valley 18z-00z.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 11 PM PDT this evening 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.
Winter Storm Watch from this evening through Friday evening for
Burney Basin / Eastern Shasta County-Mountains Southwestern
Shasta County to Western Colusa County-Northeast
Foothills/Sacramento Valley-Shasta Lake Area / Northern Shasta
County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.
&&
$$
