936
FXUS66 KSTO 281958
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
1258 PM PDT Thu May 28 2026
For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.
.KEY MESSAGES...
-Shower and isolated thunderstorm chances today, with the highest
chances across the mountains and north of I-80. Slight chance
for showers/t-storms on Saturday in the NE foothills, Burney
Basin, Lassen NF and adjacent higher terrain.
-Trend toward drier and warmer weather end of the weekend into
early next week, with Moderate HeatRisk potential.
&&
.DISCUSSION...
...Today through Saturday...
Upper level low pressure continues to bring weather impacts to
NorCal today. Current GOES-18 Satellite imagery reveals the low
just to the south of the Delta, with wrap-around cloud bands of
mid-level water vapor stretching into portions of Shasta and
Tehama Counties. Stockton and Modesto Airports are currently
observing light rain just to the east of the low pressure.
Elsewhere, scattered to broken mid-level clouds are helping keep
temperatures in the upper 50s to mid 60s across the Valley. We
will likely some additional breaking of cloud coverage as we move
through the early afternoon, which will allow for surface warming
and slight destabilization of the airmass leading to another round
of isolated showers and thunderstorms developing. Current high
resolution models suggest around 1-3 PM we could see storms
beginning to develop in our higher terrains then eventually move
into portions of the Valley. Best chances for storms will be in
the northern/central Sacramento Valley, Sierra and southern
Cascades, and the Coastal Range. Daytime heating/sunshine will
likely determine the extent and coverage of the thunderstorms
around the area. Another wave of precipitation is forecast to move
into the northern Sacramento Valley in the evening where a few
rumbles of thunder will be possible, but looks to be light to
moderate at times rain.
Lingering light showers are possible on Friday, but most of the
"heavier" activity will be moving out of the region as the closed
low moves eastward into the Four Corners Region. Cloud coverage
will help keeps temperatures seasonably cool once again tomorrow.
By Saturday, slight warming is forecast to begin as the low moves
further out of the area and into Rockies. An upper level trough
may develop offshore Saturday, bringing some instability to
portions of the northern Sacramento Valley, Lassen NF, and Burney
where the NBM has highlighted roughly 10-15% chances of afternoon
t-storms and showers. Confidence is low on this setup, but with
enough instability and wrap-around moisture from the Colorado low
an afternoon storm cannot be ruled out. Valley temps will see a
jump and climb into the low to mid 80s, except in the Delta where
somewhat enhanced onshore flow will help temperatures stay in the
mid to upper 70s.
...Sunday and onward...
To close out May, we will see a more zonal upper level air
pattern, which will continue to promote onshore flow in the Delta
and allow for our temperatures to become the headline once again.
Outside of Delta Breeze influenced areas, temperatures will climb
into the mid 90s in the Valley by Monday through Wednesday.
Moderate HeatRisk in the Valley returns Monday and becomes more
widespread in the Valley floor Tuesday and Wednesday. Another
concern moving forward will be the return of low daytime humidity
values in the Valley, where by Sunday we could see minimum RH
values in the low to mid teens. Still a little too early for
headlining any Fire Weather dangers, but we are keeping an eye on
the forecast trends.
&&
.AVIATION...
VFR conditions outside of any showers and thunderstorms that
develop around the region today, where MVFR and IFR conditions
will develop. Best chance for thunderstorms will be in the
northern and central Sacramento Valley and mountains from around
22z - 03z Friday. Widespread rain showers develop on backside of
surface low around 09z Friday. Snow levels around 8000 feet.
Surface winds generally light through 12z Friday, where southerly
gusts up to 20 kts possible. Otherwise, surface winds below 12 kts
expected next 24 hours outside of thunderstorms.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
