755
FXUS66 KSTO 211927
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
1227 PM PDT Tue Apr 21 2026
For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.
.KEY MESSAGES...
- Storm system brings moderate to heavy rain and mountain snow,
thunderstorms, cooler temperatures and breezy winds today
through Wednesday morning. Lingering light showers and
thunderstorms into Wednesday afternoon.
- Winter Storm Warning in effect through Wednesday afternoon
- Mostly dry weather, with the potential for light mountain
showers late this week into early next week. Isolated mountain
thunderstorms possible on Saturday.
&&
.DISCUSSION...
...Today through Wednesday...
An upper level low will continue to move onshore today and into
early Wednesday, bringing widespread showers, moderate to heavy
mountain snow, gusty winds and thunderstorms to the region. Latest
afternoon radar shows scattered showers across the area, with
isolated thunderstorms developing across portions of the Valley.
Precipitation is expected to continue through the rest of the day,
with the potential for afternoon and evening thunderstorm
development. WPC guidance indicates additional precipitation
amounts of 0.25 to 0.60 inches in the Valley, with 0.50 to 1.50+
inches in the foothills and mountains.
As the upper low moves inland, that is where our greatest chance
for thunderstorms will also be across the region. Atmospheric
profiles suggest the potential for strong to severe thunderstorms
this afternoon and evening, mainly across the northern San Joaquin
Valley and adjacent foothills. Main threats with thunderstorms
will be heavy rain, dangerous lightning, small hail, and brief
funnels/weak tornadoes.
Moderate to heavy mountain snow will bring travel impacts across
the northern Sierra and southern Cascades today. A Winter Storm
Warning remains in effect above 5000 feet until 5 PM PDT
Wednesday. Heaviest snow, with potential snowfall rates of 1-2"
per hour, will be today, where some convective snow bands may
develop. Any convective snow bands that develop may also lower
snow levels briefly, so some brief, heavy wet snow showers may be
possible below 5500 feet. Additional snowfall accumulations of
up to 6-12 inches are expected above 5000 feet, with up to 18
inches at the highest peaks, and Minor accumulations of 2 inches
down to 4500 feet are in the forecast today through Wednesday.
Snow levels will lower to around 4500-5500 feet by early
Wednesday, with mostly light lingering snow showers up to 1-3
inches expected.
Shower activity decreases after Wednesday morning, with mainly
light lingering mountain showers possible through the afternoon
and early evening. There is also a 10-15% chance for
thunderstorms on Wednesday.
...Thursday through Monday...
By Thursday, generally dry conditions will overtake the area and
continue into the weekend. A trough will build in the EPAC
however, which will introduce chances for light mountain rain and
snow showers Friday through early next week. Latest NBM also
depicts a 10-25% chance for mountain thunderstorms on Saturday,
with the highest chances in Shasta County. High temperatures will
fluctuate Thursday- Sunday, with gradual warming Thursday and
Friday then gradual cooling by the weekend. Highs will be in the
60s to 70s in the Valley and foothills, with cooler low to mid 40s
to 50s for the higher elevations.
&&
.AVIATION...
A weather system is currently moving through interior NorCal,
bringing Valley rain and t-storms and mountain snow. Widespread
MVFR conditions due to low ceilings at all TAF sites next 12-18
hours. Occasional breaks in clouds will allow for rapid changes in
visibilities, and any storm that develops will lower viz/ceilings
to IFR/LIFR conditions. Best chances for t-storms through 06z
Wednesday. Snow levels around 5000 feet next 24 hours. Surface
wind gusts up to 25 knots in Valley; up to 35 knots in higher
terrain.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 PM PDT Wednesday for Lassen
Volcanic NP-Sierra (Cal-Tuo) Above 5000 ft-Sierra (El Dorado-
Amador) Above 5000 ft-Sierra (Sierra-Placer) Above 5000 ft-
Sierra (Tehama-Plumas) Above 3000 ft.
&&
$$
