197
FXUS66 KSTO 222036
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
136 PM PDT Fri Aug 22 2025

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

.DISCUSSION...

.SYNOPSIS...
Triple digit high temperatures and limited overnight relief
culminate in widespread Moderate HeatRisk and areas of Major
HeatRisk today and Saturday. As a result, a Heat Advisory remains
in effect for the Coastal Range, Delta, Valley, and adjacent
foothills until 11 pm PDT Saturday night. Elevated fire weather
conditions accompany the hot and dry conditions today and
Saturday, with near daily mountain thunderstorm chances
anticipated today into early next week. A gradual cooling trend
begins by Sunday as near normal temperatures return by late next
week.

&&

.KEY MESSAGES...

* Today - Saturday:
 - Heat Advisory remains in effect for the Coastal Range, Delta,
   Valley, and adjacent foothills through 11 pm PDT Saturday
   night.
 - High temperatures in the upper 90s to triple digits expected
   through the Valley/foothills, with limited overnight relief.
 - Probability of Valley/foothills high temperatures > 100F:
   65-100%
 - Widespread Moderate HeatRisk and areas of Major HeatRisk.

 - Elevated fire weather conditions due to isolated mountain
   thunderstorm chances along the Sierra, as well as hot and dry
   weather elsewhere, with low daytime humidity in the low teens
   to 20s and limited overnight recovery.
 - Monsoonal moisture advection will bring chances of isolated
   afternoon/evening thunderstorms to the Sierra crest from I-80
   southward.
 - Probability of mountain thunderstorm development: 10-20%

* Sunday - Next Week:
 - Gradual cooling trend from Sunday onward as Four Corners
   ridging breaks down and weak offshore troughing begins to
   develop.
 - Widespread Moderate HeatRisk through Tuesday, becoming
   primarily Minor HeatRisk from midweek onward.
 - Isolated mountain thunderstorm chances spread northward to
   include the Sierra/southern Cascades and Shasta County
   mountains as monsoonal moisture advection continues.
 - Highest mountain thunderstorm chances around 15-30% expected
   Sunday and Monday, decreasing to 10-20% through midweek.

.Changes from previous forecast...
- Highest mountain thunderstorm potential expected Sunday and
  Monday, although impacts from dry lightning outside of
  precipitation cores possible today and Saturday as well.
- A more gradual cooling trend is expected into next week with
  areas of Moderate HeatRisk lingering through Tuesday.

&&

.AVIATION...
Mainly VFR conditions expected next 24 hours across interior
NorCal. Surface winds below 12 knots, except in the Delta and
vicinity from around 00z Saturday through 08z with surface gusts
up to 25 knots.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 11 PM PDT Saturday for Carquinez Strait and
Delta-Central Sacramento Valley-Mountains Southwestern Shasta
County to Western Colusa County-Northern Sacramento Valley-
Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta
County-Southern Sacramento Valley.

&&

$$