436
FXUS66 KSTO 201916
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1216 PM PDT Sun Sep 20 2026


.KEY MESSAGES...

  - Periodically breezy winds and warming temperatures this week, with
    areas of Moderate HeatRisk in the Valley on Thursday.

  - Isolated mountain shower and thunderstorm chances (less than
    10%) in the Sierra south of Highway 50 on Monday.

  - Potential for unsettled weather and increased onshore winds
    Friday into the weekend as a system passes to our north.


&&

.DISCUSSION...
Today-Monday:
Scattered high clouds are being observed over portions of
Northern California this afternoon as a deepening offshore trough
approaches the SoCal coast. As a result, periods of breezy onshore
wind will develop today with west to southwest gusts 15 to 25 mph
mainly through the Delta. Onshore flow increases on Monday with
Delta gusts up to 30 mph and breezy winds up into the Sacramento
Valley. Additionally, as this low tracks further onshore, it will
bring chances for limited precipitation and isolated thunderstorms
(less than 10%) Monday afternoon/evening. Highest potential
exists south of US 50. Primary impacts from any thunderstorms that
develop will be new fire starts from isolated lightning strikes
and gusty outflow winds.

Tuesday-Thursday:
As the trough weakens and moves further into the Desert Southwest,
Northern California will remain under split flow aloft as heights
increase. As a result, onshore flow influence will weaken heading
into midweek as temperatures trend warmer. The warmest
temperatures of the week are currently expected on Thursday, with
areas of Moderate HeatRisk in the Delta and southern Sacramento
and northern San Joaquin valleys, however there is still some
uncertainty regarding how warm temperatures will be. Relative
humidities trend lower during this time as well.

Friday-(next)Sunday:
Heading toward the end of week/weekend period, offshore troughing
is forecast to dig down from the Gulf of Alaska. This will induce
stronger onshore winds through the Delta/Valley and enhanced gap
flow through the Coast Range. This system will also bring the
potential for unsettled weather in the form of light shower
chances over Shasta County mountains on Friday. Temperatures are
also forecast to trend cooler Friday into the weekend with Valley
highs in the 80s.


&&

.AVIATION...
VFR conditions expected through 18z Monday. Winds at the TAF
sites will be less than 12 kts, but west-southwest gusts to 15-20
kts are possible in the Delta after 23Z Sunday. Gusts then
increase up to 25 kts after 06Z Monday.


&&

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

$$