230
FXUS66 KSTO 011952
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1252 PM PDT Mon Sep 1 2025

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

.DISCUSSION...

.SYNOPSIS...
Above normal temperatures and Moderate HeatRisk with areas of
Major HeatRisk continue today. 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 until 11 pm tonight for the
  southern Sacramento Valley, northern San Joaquin Valley, and
  adjacent foothills locations.

* Today:
 - Above normal temperatures expected with widespread Moderate
   HeatRisk and areas of Major HeatRisk in the Valley/foothills.
 - Probability of Valley/foothills High Temperatures > 100F today:
   60-95%
 - Dry weather persists today 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 (10-30%) 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...
- Slight increase in thunderstorm potential for Tuesday afternoon
  and evening

&&

.AVIATION...
VFR conditions 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 15-20 kt until 03Z
Tue. Areas of scattered cumulus clouds after 09z Tue through 18z
mainly over the Sierra and adjacent foothills with a chance of
isolated showers and virga.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 11 PM PDT this evening for Motherlode-
Northern San Joaquin Valley-Southern Sacramento Valley.

&&

$$