889
FXUS66 KSTO 121939
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1239 PM PDT Sat Sep 12 2026

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


.KEY MESSAGES...

  - Critical fire weather conditions through Monday afternoon due
    to gusty winds and low daytime humidity

  - Red Flag Warning in place for portions of the Sacramento
    Valley and adjacent foothills until 5 PM PDT Monday

  - Notable cool down over the weekend, with near to below normal
    temperatures expected

&&

.DISCUSSION...

Today-Monday:
Clear and sunny skies are being observed today as an upper low
passes through the PacNW resulting in increased onshore flow and
gusty southerly winds today, alongside cooler temperatures. Today,
the strongest winds are forecast through the Delta, vicinity
Valley locations, and Sierra Crest with gusts up to 35 mph at
times. Many areas in and around the Delta have already observed
gusts 20 to 30 mph. Southwesterly winds will gradually weaken
heading into the overnight period, transitioning to light north
winds by early Sunday morning. North winds then strengthen through
the Valley Sunday afternoon into the evening and Monday morning,
with gusts to 35 mph at times. These winds combined low daytime
humidities and available fuels will result in periods of critical
fire weather conditions through the weekend.

As a result, a Red Flag Warning is in effect for
portions of the Sacramento Valley and adjacent foothills until 5
PM Monday. Relative humidities will be low, especially in the
warned area, around 10 to 25% during the day. Lowest daytime
humidities of the weekend period are expected on Monday.
Overnight humidity recovery is expected to be higher tonight as a
result of the onshore flow, but then trend lower as the north
winds develop. Overall, the strongest winds are expected today and
again Sunday evening into Monday morning, but probabilities for
gusts 40 mph or greater remain below 30%. Latest models show a
stronger push of north winds Monday morning, potentially lingering
into the afternoon hours which is when the lowest daytime
humidities are expected.

Tuesday-Friday:
Weak troughing will remain over NorCal, maintaining near normal
temperatures and periodically breezy winds. Be sure to follow the
forecast at weather.gov for any updates!

&&


.AVIATION...
VFR conditions prevail at TAF sites across the forecast period.
Gusty south to southwest winds expected in the Sacramento Valley
and Delta with gusts 20 to 30 kts through 12Z Sunday. Isolated
north gusts to 20 kts in the northern San Joaquin Valley through
18Z Sunday.

After 19Z Sunday, winds weaken and begin to shift out of the
north. Stronger north winds expected in the Valley after 06Z
Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 5 PM PDT Monday for Butte County Below
1000 ft-Central Colusa County Incl. I-5-Central Glenn Co &
Interstate 5-Eastern Colusa County-Eastern Glenn County-
Glenn/Colusa Coast Range Above 3000 ft-N. Sac Valley in Tehama
County-Shasta Metro-Sierra (Tehama-Plumas) 1000-3000 ft-
Sutter/Yuba counties below 1000 ft-W. Glenn/Colusa Foothills
1000-3000 ft.

&&

$$