Delevan, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

365
FXUS66 KSTO 122132
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
232 PM PDT Wed Mar 12 2025


.SYNOPSIS...
An active weather pattern continues as the first in a series of
weather systems impacts the region. Periods of moderate to heavy
rain and isolated thunderstorms, heavy mountain snow, and gusty
winds are expected to bring major travel impacts at times through
the end of the week. A brief lull in impacts is expected over the
weekend before another impactful system arrives early next week.

&&

.DISCUSSION...

*Storm #1 (Through Thursday):

A rather deep trough with an atmospheric river plume is moving
through the area. Rainfall in the Valley continues to remain
mainly north of I-80, where rainfall amounts as of 2 pm have been
around a tenth to a quarter of an inch. Heavier showers will move
through the area later this afternoon into tonight, as well as the
potential for isolated thunderstorms into the Delta and Shasta
County (5 to 15 percent probability). Heavier snow showers are
expected in the mountains with snowfall rates up to 3 to 4 inches
an hour.

With the trough becoming centered over the region by midday
Thursday, probabilities of thunderstorm development jump up to 20
to 35 percent for Thursday afternoon and early evening with
significant instability boosted by solar heating. The magnitude
of shear profiles will be limited underneath the trough, but
proximity to the trough itself may offer some localized
enhancement. Regardless, any thunderstorms that develop will be
capable of brief heavy rain, gusty winds, hail, and lightning.

Widespread wind gusts 35 to 45 mph are expected to continue
through the Delta, Valley, and foothills through this evening. A
Wind Advisory continues for those areas until 11 pm tonight. The
strongest gusts to 65 mph are possible over the mountains.

Snow levels are still expected to vary through the event,
started around 4500 to 5500 feet, but have been slow to drop from
those levels so far. These are expected to rapidly falling to
3000 to 4000 feet by late this evening, before settling around
2500 to 3500 feet by Thursday. With heaviest precipitation
expected this 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 light
accumulating snowfall as low as 3500 feet. Forecast snowfall
totals from today 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 3 inches per hour peak
around 40 to 70% along the Sierra/southern Cascades this afternoon
and evening.

*Storm #2 (Friday-early Saturday)

There will be very little lull in precipitation impacts late
Thursday evening into the overnight hours is expected. A quick
moving shortwave is will quickly bring renewed precipitation
chances. Some uncertainty still remains regarding the timing of
warm air advection as the shortwave approaches, with a slight lag
in this feature resulting in some potential for lower elevation
snowfall across Shasta County and into the upper foothills of the
Sierra/southern Cascades. Even the most generous estimates
indicate snow levels remaining around 2000 to 3000 feet at best
for much of the event, lending credence to at least some potential
for accumulating snowfall in these locations. Current
probabilities of up to 2 inches of snowfall between 2500 and 3500
feet along the Sierra/southern Cascades sit around 30 to 60
percent at this time, with some nonzero probabilities of a dusting
across the lower elevations of Shasta County, potentially reaching
Redding. As a result of the lower snow levels Winter Storm Watch
has been issued from 11 PM Thursday to 11 PM Friday for above
2000STDAFDSTOfeet for the northern mountains, northeast
foothills, northern Coastal Range foothills and southern Cascades.
A main concern with this event is impacts to Interstate 5 over
northern Shasta County.

The expected trajectory of this shortwave will likely limit
overall rainfall potential through the remainder of the Valley
and Delta, with probabilities of exceeding 0.5 inches of
precipitation around 20 to 40 percent. Attendant probabilities of
precipitation exceeding 1.0 inches for Friday continue to sit
around 30 to 60 percent across the mountains and foothills. Aside
from lower elevation snowfall potential, more appreciable snowfall
accumulations are expected above 3500 feet at this time, with
probabilities of exceeding 6 inches of snowfall around 60 to 90
percent, and additional probabilities of 50 to 70 percent for
exceeding 1 foot of snowfall above 6000 feet.

Ensemble guidance remains in good agreement that the Friday
system will be fairly progressive, as most precipitation is
expected to come to an end by Saturday morning. Additionally, a
transient period of ridging aloft building in between systems over
the weekend looks to keep Saturday dry. Despite this relative
lull, 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 (Sunday THROUGH Wednesday)...

*Storm #3 (Sunday-Tuesday):

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" Sunday-Tuesday AM: 20-50%
Valley/foothills

Probability of Snow > 12" Sunday-Tuesday AM: 60-95% above 5000`
STDAFDSTO
Probability of Wind Gusts > 40 mph Sunday: 55-90%

Probability of Thunderstorms Sunday-Monday: 10-20%

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
differs on the upper level pattern moving past the extended
forecast period, but consensus indicates dry weather continuing
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...
Periods of MVFR/IFR/LIFR expected today into tomorrow due to
periods of moderate to heavy rain, mountain snow, and low ceilings
through 18Z Thursday. Southerly winds gusting 30 to 40 kts
through the Valley/foothills will persist though 03Z Thursday,
with gusts 55 to 65 kts anticipated along the Sierra crest.
Isolated thunderstorm chances increase tomorrow across the Valley
and Sierra foothills, with a 20-40% chance of development between
18Z-03Z.




&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 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.

Winter Storm Watch from Thursday 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.

Wind Advisory until 11 PM PDT this evening for Carquinez Strait
and Delta-Central Sacramento Valley-Motherlode-Mountains
Southwestern Shasta County to Western Colusa County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.

&&

$$