872
FXUS66 KSTO 242048
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
148 PM PDT Thu Jul 24 2025


.DISCUSSION...

.SYNOPSIS...
Below-normal temperatures and breezy onshore winds. Chances for
afternoon and evening mountain thunderstorms today through the
weekend, with chances for isolated showers over the Valley and
Sierra foothills through Friday.

&&

.KEY MESSAGES...

*  Today-Friday:

 - Afternoon highs in the 80s and low 90s throughout the Valley
   as below normal highs continue this week.
 - Onshore winds will be breezy to gusty through the Delta and
   into the Valley.

 Thunderstorms:
 - Chances (15-30%) for isolated to scattered mountain showers
   and thunderstorms during the afternoon and evening hours.
 - As an offshore low pressure system moves inland today, storms
   that develop over the mountains will generally move to the northwest,
   with the majority of thunderstorm activity occurring outside
   of interior Northern California today.
 - There is increasing confidence that a few stray showers will
   develop over the Sierra foothills and portions of the
   Sacramento Valley during the overnight hours tonight into
   Friday morning.
 - On Friday, as the low moves further south, storm motion over
   the mountains will be largely southeasterly over the Coastal
   Range, allowing for a 15-20% chance of isolated thunderstorms
   in the northern Sacramento Valley. Storm motion over the Sierra
   will be largely northeast/westerly, but individual storms will
   be subject to terrain influences.
 - The majority of thunderstorms will be wet, with the potential
   for isolated dry lightning.
 - Elevated fire weather conditions are expected in the mountains
   through Friday and into the weekend due to the lightning
   threat.
- Any strikes outside the main precipitation core will pose the
   threat for fire starts.

* Saturday-Sunday:
 - Chances (15-20%) for isolated to scattered mountain showers and
   thunderstorms continue on Saturday and Sunday remaining largely
   confined to the Sierra, with the highest potential on
   Saturday.
 - Storms are expected to form along the Sierra crest and move
   northeastward on Saturday, resulting in most of the activity
   occurring outside of interior Northern California.
 - Thunderstorm chances decrease on Sunday over the Sierra to
   10-15%.
 - Temperatures are expected to remain below-normal through the
   weekend with a slight warming and drying trend beginning on
   Sunday.
 - Onshore winds will be breezy to gusty through the Delta and
   Valley, especially during the late afternoon and evening
   hours.


* Long Term:
 - Cluster Analysis supports heights flattening out as riding over
   the Pacific Northwest encroaches into Northern California early
   next week.
 - Temperatures will follow a warming trend Monday through
   Wednesday, with weaker but still breezy onshore winds compared
   to the weekend.


.Changes from previous forecast...
 - Increased potential for isolated foothills/Valley showers
   overnight Thursday into Friday.
 - 10-20% chance of isolated showers and thunderstorms in the
   northern Sacramento Valley on Friday.


&&

.AVIATION...

Mostly VFR conditions expected over the next 24 hours across
Interior NorCal. Isolated thunderstorms may cause MVFR/IFR
conditions along the Sierra Crest this afternoon and evening. There
is a slight chance for the storms to move over the Valley as
showers this evening and overnight, bringing potential for brief
periods of MVFR to portions of the Valley as well. For the
Valley, south to southwest surface winds generally less than 12
kts with gusts up to 15 to 20 kts through 03z Friday and again
after 22Z Friday. For the Delta vicinity, sustained winds 10 to 20
kts with gusts 20 to 30 kts at times. Non-zero chance (less than
10%) for a few low clouds around 1000-2000 ft from 12Z to 16Z
Friday in the Delta and adjacent Valley locations.

&&

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

$$