858
FXUS66 KSTO 052149
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
249 PM PDT Fri Sep 5 2025

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


.DISCUSSION...

.SYNOPSIS...
A pattern change will bring a continued cooling trend into early
next week, with chances for showers and isolated thunderstorms.
Smoke from recent fire starts may impact local air quality.Breezy
onshore winds are possible at times. Humidity levels will trend
higher into next week, with good overnight recoveries.
&&

.KEY MESSAGES...

* TODAY:
 - High temperatures continue on a gradual cooling trend with
   Widespread Minor today and tomorrow
 - Smoke form recent fire starts will continue to impact air
   quality in the area. Visit Airnow.gov to check the Air Quality
   Index for your area.

* SATURDAY AND SUNDAY:
 - Mostly calm and cooler weather is expected on Saturday as an
   upper level trough moves out of the area. Higher temperatures
   will continue to cool into the mid to upper 80s, with mostly
   mid 80s for the Valley by Sunday.
 - Precipitation in the area will be limited to Saturday
   afternoon/evening over the northwestern portion of Shasta
   County, where there will be a slight chance (15%) of
   thunderstorms.

 - An upper level level low developing off the Pacific Northwest
   Coast by Sunday will remain slightly offshore and will help
   enhance onshore flow, with periods of breezy winds in the Delta
   and vicinity.
 - Sunday late evening/overnight shower chances in the northern
   Coastal Range and northern Sacramento Valley. Daytime humidity
   levels surge into the mid 30s to mid 40s across the Valley,
   with decreasing fire weather concerns.

* MONDAY - THURSDAY:
 - Precipitation chances continue on Monday - Thursday as an upper
   level trough is forecast to move inland over NorCal.
- Monday precipitation chances are highs in the northern
    Sacramento Valley and adjacent higher elevations.
- Forecast details will likely change over the next few days,
    especially specific rainfall amounts.
 - Uncertainty particularly exists on thunderstorm formation
- Ensembles confidence remains high on the overall upper level
    pattern.
        - Available moisture will be the limiting factor
 - Currently, mostly scattered light rain showers with a few
   embedded thunderstorms seems most likely; A great deal of
   uncertainty remains on total amounts. Areas in the northern
   Sacramento Valley, adjacent southern Cascades northern Sierra
   and northern Coast Range stand the best chances to see
   measurable precipitation at this time.
- NBM probabilities for 0.25" of rain are around 30-50% for the
    likely areas previously mentioned.

.CHANGES FROM PREVIOUS FORECAST...
- Slight chance (15%) for thunderstorms Saturday
  afternoon/evening for northwestern Shasta County.

&&

.AVIATION...
VFR conditions are expected over the next 24 hours. General
afternoon winds will be 10-15 kts across the Sacramento Valley
with gusts up to 15-25 kts, strongest in the Delta until 03z Sat
with lingering gusts through the Delta through 12z Fri. Chances
for marine intrusion again with cloud ceilings 1-2 kft across the
Delta and portions of the Sac. Valley from 11z to 16z Sat. &&

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

$$