954
FXUS66 KSTO 062046
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
146 PM PDT Sun Sep 6 2026

For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.


.KEY MESSAGES...

  - Drying and warming trend Monday through Thursday, with areas
    of Moderate HeatRisk Wednesday and Thursday.

  - Slight chance (15%) of thunderstorm on Wednesday over the
    Sierra crest, mainly south of US-50.

  - Cooldown in temperatures and breezy onshore winds Friday into
    next weekend.

&&

.DISCUSSION...Upper-level trough extended from British Columbia to
Northern California has begun to weaken and shift east-northeast
today. Latest Visible satellite imagery depicts mid/high- level
clouds streaming eastward across Shasta County and cumulus clouds
over the Sierra Nevada this afternoon, while mostly clear skies
elsewhere in interior NorCal. Thunderstorm are expected to remain
north of the forecast area, although a storm or two could be
possible near the Shasta and Siskiyou County border this
afternoon. Otherwise, generally dry weather and slightly warmer
temperatures is forecast for today. Breezy onshore winds are
expected this afternoon into early evening, with gust up to 25 mph
possible in the Delta, with up to 35 mph over the Sierra.

High pressure will begin to build into the West Coast with 850 mb
warming for Monday, Labor Day. Expect dry and warmer temperatures,
with high back to near-normal for this time of the year. Daytime
temperatures are forecast to be generally in the mid 80s to low
90s for the valleys. Breezy north winds with gusts up to 25 mph
is expected along the I-5 corridor on Monday. With daytime humidity
in the mid 20s percent, fire weather threat remains low.

A drying and warming trend is expected through Thursday as
anomalous high heights from the upper-level ridge across the
Dessert Southwest nose in from the east. Significantly warmer
temperatures are expected for mid week, with highs peaking in the
90s into 100s on Wednesday and Thursday. Resulting in increasing
heat risk across interior NorCal, with areas of Moderate HeatRisk
Wednesday and Thursday. Afternoon relative humidity values will
be likely in the teens to low 20s percent, especially on
Wednesday. However, winds will be light and diurnal terrain
driven. There remain a slight chance (15%) for isolated
thunderstorms on Wednesday over the Sierra crest, especially south
of US-50.

Ensembles and operational model guidances are in an overall
agreement with an upper-level trough driving southward from the
Pacific Northwest on Friday. This will bring a cool down in
temperatures Friday into next weekend. However, there is
uncertainties with the position of the low and if there will be
any impacts to our area.

There is a low confidence in the forecast for mid to late next
week as the models continue to have a disagreement regarding the
position of the cutoff off California and the remnants of Marie.
The GFS and ECMWF ensembles suggest PWAT anomaly generally about
150-200% above-normal across the area. Currently there is a
potential for showers and isolated thunderstorms over the Sierra
for mid-week. Meanwhile, temperatures trend warmer, with near to
above normal by mid to late next week.

&&

.AVIATION...Prevailing VFR conditions for the TAFs period.
Valley winds light/VRB, becoming south to west around 5-10 kts
after 22Z. Some occasional higher gusts are possible for the Delta
and Valley. Winds over the Sierra W-SW at 10-20kt, with
occasional gusts at 20-35 kts. Winds are expected to weaken this
evening, with northerly developing along the I-5 corridor on
Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$