633
FXUS66 KSTO 191913
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1213 PM PDT Sat Sep 19 2026

.KEY MESSAGES...

  - Seasonable temperatures and dry conditions persist over the
    weekend with generally offshore winds.

  - Isolated mountain thunderstorm chances along the Sierra south
    of Highway 50 on Monday.

  - Dry weather remainder of next week with gradual warming trend
    through the middle of the week.

&&

.DISCUSSION...

This Weekend:
Weak ridging aloft will continue to build in over the weekend
with a deepening offshore trough then expected to approach the
West Coast later in the day on Sunday. Resultant weather impacts
through the weekend are expected to remain minimal with seasonable
high temperatures in the 80s to low 90s and dry conditions. Light
to occasionally breezy north to east winds gusting 15-20 mph at
times look to shift toward onshore south to west winds on Sunday
as the trough arrives. Low daytime humidity values and limited
overnight recovery are anticipated today into Sunday morning with
generally improving conditions later Sunday as onshore flow
resumes.

Next Week:
With ensemble guidance in general agreement on a more southerly
track of the early to week trough, mountain thunderstorm chances
continue to trend further southward as well. Isolated thunderstorm
chances remain nonzero, but less than 10%, with highest potential
now anticipated south of the Highway 50 corridor. While coverage
will likely be limited at best, primary impacts from any
thunderstorms that develop will be new fire starts from isolated
lightning strikes and gusty outflow winds.

As the trough oscillates over SoCal and the Desert Southwest and
generally weakens across the remainder of the week, interior
NorCal is on track to remain underneath diffuse split flow aloft.
This will generally usher in a period of lighter onshore winds,
and with rising heights aloft, slightly warming temperatures into
the mid to late week period. While there is uncertainty in the
exact details of the warming next week, areas of Moderate HeatRisk
will be possible in the Valley and Delta on Wednesday and
Thursday. Heading toward the following weekend, offshore troughing
is forecast to dig down from the Gulf of Alaska, inducing
stronger onshore flow and introducing cooler temperatures, as well
as a potential shift toward a more unsettled weather pattern.

&&

.AVIATION...
VFR conditions expected through 18z Sunday. Winds at the TAF
sites will mainly be less than 12 kts, but a few west-southwest
gusts to 15-20 kts are possible in the Delta after 23Z Saturday.
Downsloping winds through the Sierra will also gust 20-30 kts
after 06Z Sunday. Winds are forecast to weaken after to 15Z
Sunday.

&&

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

$$