Excessive Heat and Heat in California, September 6 to 9, 2021

Area Forecast Discussion
National Weather Service Hanford CA
315 AM PDT Mon Sep 6 2021

.SYNOPSIS...
Triple digit heat returns to much of central California by this
Labor Day, with hot and dry conditions continuing into the middle
of the week. Temperatures will trend slowly downward after
Wednesday, and highs are expected to be near normal for this time
of year by the start of next week. Moisture moving in from the
south will bring a chance for some thunderstorms in the Sierra
Nevada and Kern County mountains and desert Thursday and Friday.

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.DISCUSSION...
Mostly clear, dry and now hot across the Central California
Interior as a ridge dominates the region. With minimal onshore
maritime support, the heat is now upon us as heat advisories and
excessive heat warnings now in place. Area fires will find little
support under the developing ridge pattern as the flow aloft may
push smoke back into the valley during the week. Based on short
term weather models, the ridge pattern will be strong enough to
meet heat criteria today and Tuesday. With such a strong ridge,
it may be hard to dislodge the high as the heat may continue into
the midweek period. Heat-wave starting this Labor-Day and now
expected to continue through Wednesday evening.

Ensemble models are almost unanimous in placing a strong ridge
pattern over the West for another heat-wave. Being a blocking
high, confidence is high that an area of weakness over the Eastern
Pacific will be forced to ride over the ridge pattern. Therefore,
any cooling from the area of weakness will not affect Central
California as the heat will not continue through at least
Wednesday. The heat products have been extended through Wednesday
as NBM heat risk analysis increases its confidence in persistent
heat through at least midweek. Probability of exceedance across
the Central California Interior for values at and above 100
degrees is very high. While Probability of exceeding 105 degrees
is highly likely across the Desert, the San Joaquin Valley
struggles to obtain more than 30 percent over the warmer
locations. Therefore, will maintain the current wording of
Advisory for the Valley as Warning criteria will be met across
the Desert.

Long term ensemble analysis is showing minimal error in
maintaining the blocking High over the West for most of the week.
Ensembles error analysis remains low even when a disturbance drops
from the Gulf of Alaska later this week. In the meanwhile, the
placement of the blocking high over the Four Corners region will
increase the southerly wind and begin allowing a surge of
monsoonal moisture to spread northward. While moisture will spread
north toward Central California, uncertainty exist as the its
northward extent. Will continue to mention precipitation over the
Sierra Nevada and Tehachapi Range. At the moment, any further
penetration seems unlikely as the moisture will shift eastward if
the Gulf of Alaska disturbance does manage to move the high and
the steering flow of the moisture. Yet, for now could see possible
convection toward the end of this work week.

&&

.AVIATION...
In the Sierra Nevada and Kern County mountains, areas of MVFR
visibilities, with local mountain obscured IFR visibilities, are
expected due to smoke and haze near active wildfires through at
least the next 24 hours. In the San Joaquin Valley, MVFR
visibilities are likely at times due to haze.

&&

.AIR QUALITY ISSUES...
On Monday September 6 2021... Unhealthy in Fresno and Kern
Counties. Unhealthy for sensitive groups in Kings, Madera and
Tulare Counties and Sequoia National Park and Forest. Further
information is available at Valleyair.org

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.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 8 PM PDT this evening for
CAZ179>189.

Heat Advisory from noon to 8 PM PDT Tuesday for CAZ179>189.

Heat Advisory from noon to 9 PM PDT Wednesday for CAZ179>189.

Excessive Heat Warning from noon today to 9 PM PDT Wednesday for
CAZ198-199.

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Public/Aviation/Fire Wx...Molina
PIO/IDSS/Social Media.....BSO

weather.gov/hanford