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.

&&



$$