105
FXUS66 KSTO 312122
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
222 PM PDT Sun Aug 31 2025

.DISCUSSION...

.SYNOPSIS...
Above normal temperatures and Moderate HeatRisk with areas of
Major HeatRisk continue through Monday. A progressive weather
system will bring increasing thunderstorm chances to the region
Tuesday and Wednesday as temperatures then trend more seasonable
from midweek onward.

&&

.KEY MESSAGES...

* Heat Advisory now in effect from 12 pm Monday - 11 pm Monday
  night for the southern Sacramento Valley, northern San Joaquin
  Valley, and adjacent foothills location.

* Today - Monday:
 - Above normal temperatures expected with widespread Moderate
   HeatRisk and areas of Major HeatRisk in the Valley/foothills.
 - Probability of Valley/foothills High Temperatures > 100F:
   50-90%, highest on Monday
 - Dry weather persists with daytime humidity into the teens to
   low 20s. Some single digit RH values possible in the Valley.

* Tuesday - Wednesday:
 - Weather system tracks northward along the California coast into
   the middle of the week, bringing a gradual cool down and the
   return of periodically breezy onshore winds.
 - Slight (10-20%) chance of afternoon/evening isolated
   thunderstorms as the system moves through. Highest chances on
   Tuesday.
 - Low (5-10%), but nonzero, chance of overnight thunderstorms
   Tuesday night into Wednesday AM.
 - Lingering uncertainty in the location of potential thunderstorm
   development, although highest chances remain across the
   mountains.

* End of the Week:
 - Broad troughing aloft expected to remain in place with slight
   variations in location and orientation.
 - Seasonable to slightly below normal temperatures forecast across
   interior NorCal by next weekend as breezy onshore flow
   persists.

.Changes from previous forecast...
- Heat Advisory now in effect from 12 pm Monday through 11 pm
  Monday evening.
- Tuesday-Wednesday thunderstorm chances persist, although
  moderate uncertainty in the location and timing of potential
  thunderstorm development continues to linger.

&&

.AVIATION...
VFR conditions and mainly clear skies are expected over the next
24 hours. Winds will be generally 10kt or less, except for the
northern Sacramento Valley, with winds up to 12 kt and gusts to 20
kt through 03Z. Cumulus build-ups over the Sierra crest are
expected through the afternoon into the early evening.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 11 PM PDT Monday for Motherlode-
Northern San Joaquin Valley-Southern Sacramento Valley.

&&

$$