916
FXUS66 KSTO 031020
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
320 AM PDT Mon Aug 3 2026

.KEY MESSAGES...

 - Heat Advisory in effect from 10 AM this morning through 10 PM
   tonight for the Sacramento & northern San Joaquin Valleys and
   foothills of the Sierra.

 - Elevated Fire Weather Conditions in the northern Sacramento
   Valley and surrounding terrain, Burney Basin, and Sierra
   Foothills through Monday due to hot temperatures, low
   humidities, and breezy winds.

 - Widespread Moderate HeatRisk persists into the week ahead
   across the Valley and Foothills. Hottest temperatures expected
   through Monday, although additional warming anticipated late in
   the week.

&&

.DISCUSSION...

***Early Monday Morning Update***

Widespread Moderate HeatRisk with areas of Major HeatRisk today
have lead to issuance of a short-term Heat Advisory for the
Sacramento Valley, northern San Joaquin Valley, and foothills of
the Sierra. Overnight model runs and warmer than forecast low
temperatures have led to product issuance this morning. Hottest
temperatures of 104-108 in the northern Sacramento Valley, with
102-106 elsewhere.

Today-Tuesday...

Split flow aloft persists over interior NorCal as the region
remains sandwiched between troughing across the Pac NW and ridging
across SoCal and the Desert Southwest. This pattern effectively
limited onshore flow and induced some offshore flow to northern
portions of the forecast area as well. As a result, overnight low
temperatures in the northern Sacramento Valley and Sierra thermal
belts remained elevated in the 70s. With the Pac NW trough
expected to eject eastward into Monday, little pattern change is
expected until Tuesday. Another period of breezy north winds is
anticipated overnight into Monday morning, with gusts 20 to 30 mph
possible along and west of the I-5 corridor and north of I-80.

Widespread triple digit high temperatures were observed on
Saturday throughout the Valley and another afternoon of similar to
slightly warmer temperatures is anticipated. Given the continued
depressed onshore flow and periodically breezy offshore flow in
the north Valley, overnight low temperatures are expected to
follow similar trends both tonight and Monday night. Current
probabilities for high temperatures greater than 100F sit around
70-95% for the Delta, Valley, and lower foothills. Additionally,
50-80% probabilities of high temperatures greater than 105F are
forecast for the northern Sacramento Valley with 15-30%
probabilities through the remaining Valley. As a result, moderate
HeatRisk is expected prevail area wide. The combination of low
daytime humidity values into the lower teens and upper single
digits, limited overnight humidity recovery, and periodically
breezy to gusty winds will continue to introduce elevated fire
weather conditions to the northern Sacramento Valley and
surrounding terrain, Burney Basin, and Sierra foothills through
Monday.

Wednesday through next weekend...

Ensemble guidance across the mid to late week period has begun to
shift as the Pac NW trough ejection is being better resolved. The
ridge axis that was forecast to center over the Desert Southwest
is now showing indications of a westward shift to center over the
Great Basin and SoCal. This shift in the upper level pattern will
introduce rising heights aloft to interior NorCal and potential
for a weaker onshore flow signal. While A slight 1-3 degree cool
down is likely Wednesday-Thursday as the pattern becomes more
ridge dominant, additional warming with limited overnight relief
and a return to widespread Moderate HeatRisk is possible late week
into next weekend. Despite marginal humidity recovery
improvements for Delta Breeze influenced locations, low daytime
humidity and poor overnight recovery is likely to continue for
much of interior NorCal throughout the extended forecast period.

&&

.AVIATION...

VFR conditions are expected to prevail over the next 24 hours. Winds
generally remain 12 kts or less at TAF sites from Interstate 80
southward. West to southwest gusts up to 18 kts in the Delta from
00Z until 12Z Monday. North to west winds increase through the
northern Sacramento Valley and Shasta County mountains after 03Z
Monday, with periodic gusts 15 to 25 kts through 21Z Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 10 AM this morning to 10 PM PDT this evening
for Butte County Below 1000 ft-C. San Joaquin County including
Stockton-C. Solano County including Fairfield-C. Stanislaus
County including Modesto-C. Yolo/NE Solano including Woodland-
Central Colusa County Incl. I-5-Central Glenn Co & Interstate 5-
Central Motherlode 1000-3000 ft-E. Diablo Range Above 1000 ft-
Eastern Colusa County-Eastern Glenn County-N. Motherlode 1000-
3000 ft-N. Sac Valley in Tehama County-NE San Joaquin Valley
Below 1000 ft-Sac Metro/W. El Dorado/Amador County-Sacramento
County Delta-San Joaquin County Delta-Shasta County Foothills
1000-3000 ft-Shasta Metro-Sierra (Tehama-Plumas) 1000-3000 ft-
Southern Motherlode 1000-3000 ft-Sutter/Yuba counties below 1000
ft-Tracy Triangle Below 1000 ft-W Tehama Co Foothills 1000-3000
ft-W. Glenn/Colusa Foothills 1000-3000 ft-W. Stanislaus County
Above 1000 ft & I-5-W. Yolo County including Capay/I-505-Yolo /
Solano County Hills.

&&

$$