499
FXUS66 KSTO 302038
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
138 PM PDT Sun Jun 30 2024

.SYNOPSIS...
A general warming trend begins today, culminating in dangerous
heat and widespread major HeatRisk with areas of extreme HeatRisk
from Tuesday into next weekend. Critical fire weather conditions
are also anticipated in the Sacramento Valley and adjacent
foothills from late Monday through Wednesday.

&&

Key Points
- Long-duration, major heat event expected this week impacting
  holiday outdoor events.
- Excessive Heat Warning remains in effect for the Valley, Delta
  and foothills from Tuesday morning through Saturday evening.
- Red Flag Warning is in effect for the western side of the
  northern and central Sacramento Valley and adjacent elevations
  below 3000 feet late Monday through Wednesday evening.

.Discussion...
Satellite imagery depicts broad troughing aloft clipping the
region today. Widespread 90s to around 100 degrees are anticipated
in the Valley and foothills this afternoon. Occasional gusts of
15 to 25 mph will remain possible through the early evening while
the trough axis is overhead. A brief instance of an isolated
shower or thunderstorm cannot be completely ruled out this
afternoon and evening across portions of Plumas County, but
thunderstorm activity will likely remain outside of the forecast
area per HREF guidance. NBM depicts less than 5 to 10% probability
of thunderstorm development this afternoon and evening.

Ensembles and clusters show strong, anomalous ridging building
into NorCal from the eastern Pacific this week resulting in a
long-duration heat event. By Monday, daytime temperatures will be
in the 100 to 105 range across the Valley. Temperatures will
continue to warm on Tuesday and Wednesday, with widespread triple
digits ranging from 100 to 110 degrees in the Valley and adjacent
foothills. NBM probabilities indicate a 60-90% chance of high
temperatures greater than 105 degrees Tuesday- Wednesday. Little
relief is expected overnight with lows forecast in the upper 60s
to around 80. As a result, widespread major HeatRisk and areas of
extreme HeatRisk look to arrive on Tuesday and remain in place
into at least next weekend. This level of HeatRisk is very
dangerous to anyone without proper hydration or adequate cooling.
Strongly consider canceling outdoor activities. An Excessive Heat
Warning remains in effect for the Valley, Delta and foothills from
Tuesday morning through Saturday evening.

Areas of gusty northerly winds are expected throughout the
Sacramento Valley and adjacent foothills from late Monday night
through Wednesday, with gusts up to 30 mph. The strongest winds
are expected on Tuesday, especially along western portions of the
northern and central Sacramento Valley. Afternoon minimum
humidities in the single digits to low teens are anticipated on
Tuesday and Wednesday. Overnight humidity recovery looks to remain
poor as well, especially across the northern and central
Sacramento Valley. The combination of gusty winds and low humidity
will lead to critical fire weather conditions. A Red Flag Warning
remains in effect from 11 PM Monday through 8 PM Wednesday.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

Ensemble guidance indicates a slight eastward transition of the
eastern Pacific ridge through the late week period as the ridge
axis looks to become centered over NorCal. Therefore, the long-
duration heat event is projected to continue through the extended
period. Resultant widespread high temperatures in the triple
digits are expected from Thursday through Sunday across the Valley
and adjacent foothills, with widespread Major HeatRisk and areas
of Extreme HeatRisk. Overnight lows will mainly be in the mid 60s
to near 80, warmest in the foothills. Daytime temperatures may
trend slightly downward on Sunday, but will remain hot. In
addition, the extended period of very hot and dry conditions will
bring elevated fire weather concerns through the forecast period.

&&

.AVIATION...

VFR conditions next 24 hours. Local northwesterly surface wind
gusts 15-25 kts northern Sacramento Valley thru 06Z Monday, and
aft 15Z Monday. Local southwest gusts 20-30 kts vicinity west
Delta after 00Z Monday, otherwise surface wind gusts generally
below 12 kts.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 PM Monday to 8 PM PDT Wednesday for
Carquinez Strait and Delta-Central Sacramento Valley in Glenn,
Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-
Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-
Northern Sacramento Valley to Southern Tehama County Line Below
1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes
portions of Shasta-Trinity and Butte Units-Southeast Edge Shasta-
Trinity NF and Western Portions of Tehama-Glenn Unit-Southern
Sacramento Valley in Yolo-Sacramento Far Western Placer,
southern Sutter and Solano County Below 1000 Ft.

Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT Saturday
for Carquinez Strait and Delta-Central Sacramento Valley-
Motherlode-Mountains Southwestern Shasta County to Western
Colusa County-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&

$$