267
FXUS66 KSTO 212032
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
132 PM PDT Thu Aug 21 2025

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



.DISCUSSION...

.SYNOPSIS...
Well above normal temperatures are expected today through
Saturday and 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 early next week
over the Sierra.

&&

.KEY MESSAGES...

* Today:
 - Above normal temperatures expected with widespread Valley
   triple digits and Moderate HeatRisk.
 - Periodically breezy north winds today may provide localized
   enhanced drying over the northern Sacramento Valley and 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 late 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 on Friday. Thunderstorm chances expand northward across
   the Sierra crest on Saturday and through early next week.
   Current models show a lack of forcing that would result in a
   larger thunderstorm threat. Storms are expected to form along
   the crest and move to the north and/or east.

 - The threat for thunderstorms and isolated dry lightning outside
   of main precipitation cores will lead to elevated fire
   concerns over the Sierra Friday through the weekend.

* 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 (15-30%) over the
   Sierra through early next week.

.Changes from previous forecast...
- High temperatures have trended up a few degrees for today and
  tomorrow
- Increased thunderstorm potential over the weekend and early next
  week
- Mountain thunderstorms Friday through the weekend will lead to
  elevated fire weather concerns due to the threat for isolated
  dry lightning outside of main precipitation cores

&&

.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 00z Friday through 12Z Friday.

&&

.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.

&&

$$