464
FXUS66 KSTO 012101
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
201 PM PDT Mon Jul 1 2024

.SYNOPSIS...
Widespread Major to Extreme HeatRisk from Tuesday into next
weekend. Critical fire weather conditions are also anticipated in
the Sacramento Valley and adjacent foothills tonight 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 much of the Sacramento Valley
  and adjacent elevations below 3000 feet tonight through
  Wednesday evening.

.Discussion...
Clear skies cover the region as very strong ridging over the
eastern Pacific edges closer. As it edges closer, temperatures
continue to warm with afternoon highs today in the low 100s with
90s and 80s across the foothills and mountains respectively. The
ridge will continue to move eastward that will lead us into our
prolonged heat event this week.

Long duration heatwave will result in widespread Major to Extreme
Heatrisk across much of NorCal beginning Tuesday and lasting into
late week. Highs of 103 to 115 are forecasted through much of the
Valley/Foothills during the week with overnight lows only mainly
in the 70s. Temperatures will be near or at 100 as late as 8PM
through midweek, so overall the main weather of the short term
will be the elevated heat concerns. As an result, an Excessive
Heat Warning remains in effect for the Valley, Delta and foothills
from Tuesday morning through Saturday evening. Wednesday is
forecasted to be hottest day of this week (although each day
carries similar HeatRisk and associated heat impacts).

This level of HeatRisk is very dangerous to anyone without proper
hydration or adequate cooling. Strongly consider canceling
outdoor activities. Do not leave young children and pets in
unattended vehicles. Car interiors will reach lethal temperatures
in a matter of minutes.

With the increased heat and breezy north winds Tuesday through
Wednesday, elevated fire weather conditions also develop for the
western portions of the Valley and parts of the Delta. Min.
daytime humidities as low as 5 to 15 percent with poor overnight
recovery near 15 to 35 percent are expected with gusts up to 30
MPH. From Sacramento to Redding westward, current probabilities
show a 40-70% chance of gusts greater than 30 MPH from tonight
through Wednesday night, highest Tuesday morning. As an result, a
Red Flag Warning has been issued for the Sacramento Valley,
generally west of Interstate 5 and elevations below 3000 feet.
Outdoor burning is not recommended as the combination of gusty
winds and low humidity can cause fire to rapidly grow in size and
intensity.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...

Ensembles and clusters remain in good agreement of the eastward
progression of a strong high pressure system over Northern
California. As a result, this prolonged heat event will continue
through Sunday before temperatures begin to cool slightly, but
will still remain hot. Widespread triple digits are expected to
continue through Monday. Some solutions in the clusters depict the
eastward transition of the high pressure system by Friday, which
will allow for a return of an onshore flow pattern. Overnight lows
through the extended periods will remain in the low 60s to low
80s, with the warmest lows in the foothills. This heat combined
with the low daytime relative humidities, fire weather concerns
will persist through the forecast period.
&&

.AVIATION...

VFR conditions next 24 hours across interior NorCal. Northwesterly
flow with surface winds generally under 12 kts. Along the western
half of the Sacramento Valley, surface winds 10-15 kts, locally up
to 20 kts, and gusts 20-30 kts at times expected through 20z
Tuesday. Southwesterly flow up to 12 kts through the Vicinity
Delta between 22z Monday-12z Tuesday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 PM this evening 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 Sunday 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.

&&

$$