Special Weather Statement, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
139 PM PDT Thu Jun 24 2021

.SYNOPSIS...
Mountain and foothill thunderstorms are expected through this
evening and again on Friday, otherwise dry. High pressure
strengthens this weekend bringing a return of very hot weather into
next week, particularly for the northern and central Sacramento
Valley.

&&

.DISCUSSION...
Mountain and foothill showers and storms began late this morning and
are expected to continue into the evening hours. Storms initially
formed along Sierra crest and have been continuing to develop to
the north with numerous lightning strikes detected. The Red Flag
Warning continues through 9PM this evening across portions of
Shasta, Tehama, and Plumas Counties due to the potential for
lightning with storms with little rainfall. Some stronger storms
will still be possible which may produce small hail and locally
gusty winds. With storm motion to the northwest, a few foothill
locations expected to see some precipitation although amounts will
be light.

Upper low off the coast which was the main driver for storms today
will continue to weaken tomorrow, although a small chance for
thunderstorms will once again be seen tomorrow afternoon, mainly
over the Sierra Nevada south of I-80 where decent elevated
instability remains.

High pressure builds in from the PacNW this weekend into next week
which will bring back hot temperatures to much of interior NorCal.
The main area of concern for this heat remains in the northern and
central Sacramento Valley and adjacent foothills where a long
duration of high daytime temperatures and warm overnight lows will
lead to dangerous heat risk for much of the population. Highs in
these areas will be range from just over 100 degrees to near 114,
with overnight lows in the 70s to mid 80s. Due to high confidence
for the extended duration of this heat event, the Watch has been
upgraded to an Excessive Heat Warning. This will span from Saturday
afternoon through Wednesday evening. A bit further south, onshore
flow will moderate temperatures a bit more near the Delta, southern
Sacramento Valley, and northern San Joaquin Valley.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Ensembles and cluster analyses continue to advertise a strong
upper level ridge over the Pacific Northwest through the weekend
and well into next week. The best potential for heat is over the
northern and central Sacramento Valley, away from any Delta-
influenced areas. Heat risk will fall into the high to very high
category for the northern and central Sacramento Valley through at
least next week Wednesday evening. High temperatures there are
expected to remain around 104-108, locally hotter. The heat risk
near the Delta, southern Sacramento Valley, and northern San
Joaquin Valley will remain in the moderate to locally high
category into next week where temperatures are not forecast to be
at hot.

The weather is expected to remain dry over much of the area
through the extended. The exception is over the northern Sierra
south of Highway 50, where some subtropical moisture advected
northward could bring afternoon showers and thunderstorms.

&&

.AVIATION...
VFR conditions expected for the next 24 hours. Scattered
afternoon thunderstorms are possible over the mountains, as well
as a few isolated showers and thunderstorms possible over far
northern Sacramento Valley. Locally gusty winds of 20 to 25 kt are
forecast in the vicinity of the Delta after 00Z Friday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM PDT this evening for Burney Basin
and Northeast Plateau in Shasta County Including Northwest
Lassen NF north of Lassen NP-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-Northern
Sierra Including Lassen NP and Plumas and Lassen NF/S West of
the Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth
Peak)-Southeast Edge Shasta-Trinity NF and Western Portions of
Tehama-Glenn Unit.

Excessive Heat Warning from noon Saturday to 10 PM PDT Wednesday
for Central Sacramento Valley-Mountains Southwestern Shasta
County to Western Colusa County-Northeast Foothills/Sacramento
Valley-Northern Sacramento Valley-Shasta Lake Area / Northern
Shasta County-Southern Sacramento Valley.

&&

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