532
FXUS66 KSTO 201841
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
1141 AM PDT Mon Apr 20 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 renewed precipitation chances in moderate
to heavy rain and mountain snow, thunderstorms, cooler
temperatures and breezy winds Today through Wednesday
- Winter Storm Warning in effect from late tonight through
Wednesday afternoon
- Mostly dry weather, with the potential for light mountain
showers late this week into the weekend
&&
.DISCUSSION...
...Today through Wednesday...
Early afternoon radar shows a band of light to moderate rain
showers moving through portions of the Coastal Range and
central/northern Sacramento Valley, mainly west of the I-5
corridor. Some RAWS sites are picking up around 0.10 to 0.25"
inches of rain over the last 6 hours, so mostly light beneficial
rain has been observed. Precipitation is expected to continue
through the rest of the day, gradually spreading eastward with
more widespread coverage by late afternoon/early evening. IVT
values of 250 kg/ms with a southerly flow, and synoptic support of
a closed low will help the Valley see beneficial rains and
snow accumulations to the Sierra Nevada, southern Cascades, and
Coastal Range.
Recent hi-resolution model trends have increased snow totals above
5000 feet slightly through Wednesday night. Overall impacts have
remained the same however, and with increased confidence of at
least Moderate winter weather impacts we have upgraded the Winter
Storm Watch to a Winter Storm Warning, effective at 2 AM Tuesday
through 5 PM PDT Wednesday. Heaviest snow, with potential snowfall
rates of 1-2" per hour, will be Tuesday through Tuesday night,
where some convective snow bands may develop. Any convective snow
bands that develop may also lowering snow levels briefly, so some
brief, heavy wet snow showers may be possible below 5500 feet on
Tuesday. Wednesday snow levels will fall to roughly 4500-5500
feet, with mostly light lingering snow showers with 1-4 inches
expected. Overall, snow accumulations of 12-18 inches above 5000
feet, 2 feet or more at the highest peaks, and Minor accumulations
of 2 inches down to 4500 feet are in the forecast today through
Wednesday.
Rain totals for most of the Valley and foothills increased with
this afternoon`s forecast run, but overall impacts look to remain
unchanged. Minor rain impacts today, then Moderate rain impacts
to the Valley and Foothills are expected tomorrow. The HRRR
suggests the heaviest rain will move onshore with the 250 kg/ms
IVT plume and closed low supporting moisture advection early
Tuesday, where moderate to heavy at times rain will be possible in
the Valley before moving into the Foothills by the late morning
and afternoon. As the main energy moves inland, that is where our
greatest chance for thunderstorms will also be across the region.
Looking at some forecast soundings across the area, shear values
at 0-1 and 0-6km are not overly impressive, nor is forecast CAPE
values at this time, however with the closed low over the area the
potential for some weak rotation exists. Main threats with
thunderstorms will be brief heavy rain, dangerous lightning, small
hail, and a brief funnel/weak tornado. Valley rain will begin to
taper off by Wednesday afternoon with light lingering rain showers
possible through the evening.
...Thursday through Sunday...
By Thursday, mostly clear and dry conditions will overtake the
area and continue into the weekend. A trough will build in the
EPAC however, which will introduce a light shower chance to our
higher terrains in the Sierra and southern Cascades Saturday and
Sunday. Overall precipitation impacts look to be little to none at
this point, as the trough will eventually move inland in SoCal by
early next week. High temperatures will fluctuate Thursday-
Sunday, with gradual warming Thursday and Friday then gradual
cooling by the weekend. Highs will be in the 70s through this
period, with cooler low to mid 40s - low 50s for the higher
elevations.
&&
.AVIATION...
A weather system is moving through interior NorCal this afternoon
and will bring widespread Valley rain showers and mountain snow
next 24 hours. Scattered MVFR/IFR conditions expected to develop
around 00z at most TAF sites, then as we move into Tuesday morning
around 06z widespread MVFR/IFR conditions at all TAF sites. Snow
levels next 24 hours generally 6000-7000 feet; falling to
5500-6500 feet by 12z Tuesday. Surface winds gusting from south-
southwest up to 25 knots in Valley; 35 knots in higher terrain
beginning around 00z Tuesday.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 2 AM Tuesday to 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.
&&
$$
