433
FXUS66 KSTO 201942
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1242 PM PDT Wed Aug 20 2025

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

.DISCUSSION...

.SYNOPSIS...
Our warming trend continues and as a result a Heat Advisory remains
in effect for the Valley, Delta, and adjacent foothills for
Friday and Saturday for triple digit highs and widespread Moderate
HeatRisk with areas of Major HeatRisk. Elevated fire weather
conditions accompany the heat with daily mountain thunderstorm
chances Friday into next week over the Sierra.

&&

.KEY MESSAGES...

* Today - Thursday:
 - Above normal temperatures expected with widespread Valley
   triple digits and Moderate HeatRisk by Thursday.
 - Periodically breezy north winds overnight into Thursday AM may
   provide localized enhanced drying over the Nor. Sacramento
   Valley and see areas of elevated fire weather conditions from
   dry and hot weather.

* Friday - Saturday:
 - A Heat Advisory has been issued for the Valley, Delta,
   foothills and Coast Range from 11 AM Friday through 11 PM
   Saturday.
 - 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 Fri-
   Sat: 65-100%
 - Widespread Moderate HeatRisk and areas of Major HeatRisk
   expected Friday-Saturday, followed by a gradual cooling trend
   into early next week.
 - Dry weather with low daytime humidity in the teens to 20s and
   limited overnight recovery anticipated mlate week. This will
   continue periods of elevated fire weather conditions.

 - Monsoonal moisture advection will bring chances of
   afternoon/evening thunderstorms to the Sierra crest south of
   I-80 Friday into the weekend. Thunderstorm chances expand
   northward Saturday and Sunday with best chances for development
   on Saturday. Current models show a lack of forcing mechanism
   that could develop into a larger thunderstorm threat but storms
   riding the ridge and moving north and east are in play.

* Sunday to Early Next Week:
 - Slight cooling trend is expected, but widespread Moderate
   HeatRisk still persists across the Valley and foothills Sunday
   and Monday with a return to Minor HeatRisk by Tuesday.
 - Isolated mountain thunderstorm chances (10-25%) over the
   Sierra through early next week.

.Changes from previous forecast...
- No significant changes at this time.

&&

.AVIATION...

VFR conditions next 24 hours across interior NorCal. Sustained
surface winds generally at or below 12 kts, except in the Delta
with west-southwest surface winds 12-15 kts with gusts 15 to 20
kts through 16Z Thursday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM Friday to 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.

&&

$$