052
FXUS66 KSTO 212005
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
105 PM PDT Mon Jul 21 2025

.DISCUSSION...

.SYNOPSIS...
Temperatures below July normals today and through the end of the
week; narrow band of sprinkles/virga associated with frontal
boundary moving through NorCal this afternoon. Breezy to gusty
onshore winds continue. Afternoon/evening mountain thunderstorm
chances Tuesday - Friday, with best chances on Wednesday and
Thursday.

&&

.KEY MESSAGES...

*  Today:

 - Upper level low ejecting from parent trough in Canada,
   continuing to retrograde through the PacNW today. Surface
   boundary currently bringing light radar returns in portions of
   the northern/central Sacramento Valley, southern Cascades, and
   Sierra.
- Some trace amounts of rainfall observed, nothing significant
    - Activity expected to diminish in the next few hours
 - Breezy to gusty onshore winds in the Delta continue, with gusts
   up to 44 mph observed this morning
 - Afternoon high temperatures forecast to be 9 to 15 degrees
   below normal today, thanks in part to partial cloud coverage in
   some areas and enhanced Delta Breeze/onshore flow
 - Green Fire smoke output lower than last few days. Fire is
   around 54% contained with limited smoke visible on GOES-18 this
   afternoon. Hazy skies still possible near the vicinity of the
   wildfire.

*  Tuesday-Friday:

 - By Tuesday, off-shore low continues to bring breezy to gusty
   onshore winds in the afternoon and evening. High temperatures
   will continue to be below July normals by 10-15 degrees, with
   Tuesday looking to be the coolest.
 - Isolated high elevation mountains showers and t-storms will be
   possible. Main concern with any convection developing will be a
   potential lack of moisture.
- Better chances Wednesday and Thursday in the Sierra and
      Southern Cascades
    - Elevated fire weather conditions in the mountains on
      Wednesday and Thursday due to potential isolated dry
      thunderstorms
 - Ensembles continue to depict offshore troughing through Friday.
   Pattern will help keep us cooler than normal.

* Long Term:
 - Cluster Analysis depicts upper level troughing may continue
   into the weekend. Heights may flatten slightly, reducing some
   of the cooling effects for the area, with temperatures warming
   back up on Monday of next week.
- Current NBM high temp forecast around 2 to 5 degrees below
      normal for Monday of next week

.Changes from previous forecast...
 - Added elevated fire weather conditions for the mountains
   Wednesday and Thursday due to potential dry lightning/isolated
   t-storms.

&&

.AVIATION...

VFR conditions expected over the next 24 hours across Interior
NorCal with west-southwest winds with gusts up to 20-25 kts until
03z Tue with lingering 10-20 kts winds in the early morning
through 18z Tuesday over the Valley and continued gusty winds
across the Delta. Chances for low clouds around 1000-2000 feet
during the early morning hours across the Delta and Southern Sac
Valley from 08z to 16z Tue.

&&

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

$$