483
FXUS66 KSTO 131919
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1219 PM PDT Mon Jul 13 2026

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

.KEY MESSAGES...

 - Monsoonal moisture bring showers and thunderstorms to the
   Sierra with potential for Valley showers today and Tuesday.

 - Warming trend Tuesday and Wednesday with widespread Moderate
   HeatRisk, then cooler temperatures in most of the Valley
   beginning Thursday.

 - Monsoonal moisture and thunderstorm chances return this weekend.

&&

.DISCUSSION...
Southerly flow and mid-level cloud deck observed this early
afternoon across most of interior NorCal. Radar shows some light
returns in the central Sacramento Valley and in portions of the
Sierra south of 50, most likely light sprinkles or virga as
latest 24-hour precipitation totals are very light or zero across
most of the CWA. Monsoonal moisture, along with some upper level
support from an offshore trough will keep Valley light shower
chances in the forecast for the rest of the day. Mountain
thunderstorm chances will gradually increase as we move through
the rest of the afternoon, with the best chances residing mainly
south of I-80.

Thunderstorm risk will continue on Tuesday, with some nocturnal
threat early Tuesday morning mainly in the Coastal Range. Chances
then increase throughout Tuesday afternoon and evening across the
higher elevations of the Sierra-Nevada, with better chances along
and east of the crest. Cannot rule out a stray Valley/foothill
shower tomorrow either, but latest CAMs looks to keep most
activity confined within the higher elevations of the area. We
will also see Valley high temperatures climb on Tuesday and
Wednesday, with widespread Moderate HeatRisk. We currently have
widespread triple-digit high temperatures on Tuesday and Wednesday
across the Valley and foothill thermal belts.

By Thursday, onshore flow will increase in response to a weak
closed low off the PacNW coast, which will help lower heights
across the region. High temperatures will fall across most of the
Valley, except in the northern Sacramento Valley where triple-
digit highs will remain in the forecast until this weekend.
Further into the weekend, we may see additional monsoonal moisture
surges into the area, with PWAT values approaching roughly 170% of
normal by Saturday. With a ridge developing near the Four Corners
region by the weekend, this setup will once again favor
afternoon/evening mountain precipitation chances. For now, the NBM
is suggesting roughly 30% chances of precipitation south of
HWY-50 Saturday - Monday.

&&

.AVIATION...

General VFR conditions prevail across interior NorCal next 24
hours. Surface wind gusts from south to southwest around 10 to 15
kts in the Sacramento Valley, Delta and Sierra Crest until 03Z
Tuesday but lingering Delta Breeze up to 15 kts until 06Z
Tuesday.

Mid to high level clouds continue periods of BKN to OVC
conditions around 10-25 kft with isolated showers and mist with a
slight chance (5-15%) of thunderstorms over the Sierra crest and
eastward from 21Z Monday to 06Z Tuesday. Slight chance of showers
returning after 12z Tuesday across the Sacramento Valley bringing
isolated MVFR conditions if developed.


&&

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

$$