279
FXUS66 KSTO 040939
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
239 AM PDT Thu Jul 4 2024

.SYNOPSIS...
Widespread Major to Extreme HeatRisk into the middle of next
week. Elevated fire weather concerns in the Valley and adjacent
foothills due to very hot and dry conditions.

&&

Key Points
- Long-duration, dangerous heat event into mid next week,
  impacting holiday outdoor events.
- Excessive Heat Warning remains in effect for the Valley, Delta
  and foothills through 11 PM Tuesday.
- Heat Advisory remains in effect for the Sierra, southern
  Cascades, and Burney Basin from 11 AM today until 11 PM Tuesday.

.Discussion...
Anomalously strong high pressure will dominate the pattern
through the forecast period, bringing an extended period of
dangerous heat. The EFI also highlights the extreme nature of
this heat event. NBM probabilities indicate a 75-100% chance of
high temperatures of 110 deg F or higher through the northern and
central Sacramento Valley, and a 30 to 75% chance in the southern
Sacramento and northern San Joaquin Valleys Friday-Saturday.
Daytime highs will range from 105-118 degrees across the Valley,
Delta, and foothills, with 80s to around 110 in the mountains.
The hottest temperatures are still expected on Friday-Saturday.
Overnight temperatures will provide little to no relief from the
heat with lows ranging from the upper 60s to mid 80s; warmest in
the thermal belt regions of the foothills.

Widespread Major to Extreme HeatRisk is expected across the
Valley and foothills, with Major HeatRisk over the mountains.
This level of rare, long-duration extreme heat with little to no
overnight relief affects anyone without effective cooling and/or
adequate hydration. An Excessive Heat Warning remains in effect
for the Valley, Delta, and foothills until 11 PM Tuesday.
Additionally, a Heat Advisory remains in effect for the Sierra,
southern Cascades, and Burney Basin until 11 PM Tuesday. Check on
sensitive groups, stay hydrated, strongly consider canceling
outdoor activities, and stay in a cool place, including overnight.
DO NOT leave children or pets in unattended vehicles.

The extended period of very hot and dry conditions will bring
elevated fire weather concerns to the Valley and foothills. Know
your wildfire risk and have an emergency plan in advance.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Ensembles and clusters show a gradual eastward progression of the
upper high late weekend into next week, resulting in a minor
downward trend in high temperatures through midweek. High
temperatures in the 105-113 F range are still anticipated through
early next week in the Valley and foothills, with a slight cool
down closer to highs in the 100-110F range into mid next week.
Some overnight relief from the heat will be possible early next
week near the Delta Breeze influenced areas. Low temperatures into
the low to mid 60s will be possible in these areas through mid
next week, with upper 60s to mid 70s still likely through the
remaining Valley and adjacent foothills locations. In terms of
HeatRisk, widespread Major to Extreme HeatRisk is expected through
early next week, with Moderate HeatRisk near Delta influenced
areas. By mid-week, widespread Moderate HeatRisk is expected
across the region, with some areas of Major/Extreme HeatRisk
(mainly in the foothills).

&&

.AVIATION...
VFR conditions expected across interior NorCal next 24 hours.
Increasing south to west gusts to 20 kts in Delta and immediate
vicinity through approximately 00z Friday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 11 PM PDT Tuesday 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-Shasta Lake Area / Northern Shasta County-
Southern Sacramento Valley.

Heat Advisory until 11 PM PDT Tuesday for Burney Basin / Eastern
Shasta County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$