189
FXUS66 KSTO 171913
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1213 PM PDT Thu Sep 17 2026

.KEY MESSAGES...

  - Cooler weather, breezy onshore winds, and increased humidity
    today

  - Isolated shower and thunderstorm chances today, mainly across
    Coast Range, Shasta County, and southern Cascades through 8 PM

  - Warming and drying conditions Friday and over the weekend with
    near normal temperatures and general offshore flow

&&

.DISCUSSION...

Today:
Current GOES-West visible satellite imagery shows the marine
stratus intrusion lingering across much of the Sacramento Valley
in the form of low clouds, with some additional cumulus
development over the mountains. Surface observations are showing
temperatures trending approximately 5 to 10 degrees cooler than
this time yesterday afternoon. The upper level pattern features an
area of low pressure over northern California, bringing cooler
temperatures, breezy onshore (S to W) flow, higher humidity, and
isolated mountain shower/thunderstorm chances. There is a 15-20%
chance of thunderstorms over the Coast Range, Shasta County, and
southern Cascades mainly between 1 and 8 PM PDT today. Potential
impacts with any storms that develop would be lightning, possible
fire starts, gusty winds, brief heavy rain and small hail.
Forecast highs are expected to be in the 70s in the Valley and
foothills and 50s to 70s in the mountains.

Friday-Weekend:
Upper low weakens and shifts eastward with upper level ridging
then building back in Friday and Saturday bringing temperatures up
closer to normal for this time of year. Dry conditions with lower
humidity are also anticipated, along with general offshore (N to
E) flow. Localized breezes are expected in the Valley during the
day Friday and in the mountain/foothill gaps and canyons in the
overnight through early morning periods. Afternoon humidity lowers
to the 20s on Friday and down into the teens in portions of the
Valley on Saturday. Good recoveries still expected in the Valleys
with locally poor to moderate recoveries possible in the the
thermal belts and ridges.

Early Next Week:
Ensemble guidance then indicates some form of upper low off the
coast Sunday or early next week bringing a period of onshore flow
and slightly cooler temperatures before the ridge builds back in.
The National Blend of Models (NBM) currently points to a low end
chance of a shower or thunderstorm (up to 10%) over the Sierra
Nevada along and south of Interstate 80 on Monday, however
confidence is low in the details at this time. As always, be sure
to check the forecast at weather.gov/sacramento for any updates!

&&

.AVIATION...
Improvement to VFR conditions at TAF sites, except 50-80% chance
of MVFR ceilings from 11Z-17Z Friday for Sacramento area
terminals. Otherwise, breezy south to west winds persist through
06z, gradually falling below 12 kts area wide overnight. Strongest
gusts 15 to 20 kts expected through the Delta and Sierra Crest.
Winds turn northerly after 18Z Friday.

&&

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

&&

$$