671
FXUS66 KSTO 032021
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
121 PM PDT Wed Sep 3 2025

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

.DISCUSSION...

.SYNOPSIS...
A progressive weather system brings thunderstorm chances today
and Thursday mainly in the mountains. Thunderstorm coverage not
expected to be as widespread as yesterday (Tuesday). Temperatures
continue a cooling trend, with isolated areas of Moderate HeatRisk
and widespread Minor HeatRisk the rest of the week. Smoke from new
fire starts will impact local air quality.

&&

.KEY MESSAGES...

* Today and Thursday:
 - Visible satellite shows surface low over far northern
   California this afternoon
 - Synoptic scale ascent, along with moisture from the desert SW
   will bring around a 10-25% chance of thunderstorms to the
   mountains today. Best chances along the Sierra/southern
   Cascades crest. Thunderstorm coverage not expected to be as
   widespread as yesterday (Tuesday).
 - High temperatures continue on a gradual cooling trend; with
   isolated Moderate HeatRisk in the northern Sacramento Valley
   with Minor HeatRisk elsewhere.
 - Thunderstorm chances on Thursday are around 5-15%, along the
   Sierra and southern Cascades crest. Low confidence on storm
   development Thursday afternoon/evening.

* Friday - Tuesday:
 - Broad troughing aloft expected to remain in place through early
   next week with slight variations in location and orientation
   across ensembles
 - Precipitation chances enter the forecast on Monday and Tuesday,
   as upper level trough is progged to be over NorCal.
- Monday precipitation chances highest in the northern
          Sacramento Valley
        - Tuesday precipitation chances are mainly north of
          Sacramento County and in the higher elevations
- Forecast will likely change as ensembles come into better
          agreement
 - Seasonable to slightly below normal temperatures forecast across
   interior NorCal by next weekend as breezy onshore flow
   persists.

.Changes from previous forecast...
- Thunderstorm chances for Thursday slightly decreased, as well as
  coverage area
- Precipitation chances next week on Monday and Tuesday, with a
  high level of uncertainty regarding potential impacts

&&

.AVIATION...

VFR conditions are expected over the next 24 hours. Winds will be
generally 10kt or less, except near the Delta with winds up to 12
kt and gusts up to 15-25 kt into 18z Thu. Chances for local
MVFR/IFR conditions from thunderstorms over the Sierra and
Southern Cascades in the afternoon and evening until 09z Thu.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$