Flash Flood Warning 33, NWS Hanford, CA

Area Forecast Discussion
National Weather Service Hanford CA
250 PM PDT Thu Jul 25 2019

.SYNOPSIS...
A large area of high pressure will maintain widespread triple
digit heat across the San Joaquin Valley, West Side Hills and Kern
County Deserts through at least Monday. The peak of this heat
should occur this weekend. Isolated afternoon and evening
thunderstorms are possible through Friday in the Southern Sierra
Nevada.

&&

.DISCUSSION...
Another round of afternoon thunderstorms already flaring-up as
monsoonal moisture continues to surge north into the region.
While the Sierra Nevada and Tehachapi Range will keep thunderstorm
activity confined to the mountains and deserts, a few stray
showers could reach the lower foothills before sunset this
evening. Yet, with abundant moisture and smaller-scale
disturbances moving into the area, thunderstorms are very likely
outside of the San Joaquin Valley. Enough moisture, instability
and lift could support brief heavy precipitation over the favored
areas. This thinking lead to the issuance of a flash flood watch
over the deserts and mountains through 11 PM PDT this evening. In
the next few days, the trend will be to increase the heat as
advisories and watches are currently in effect, and decrease the
moisture. Therefore, while thunderstorms may still develop on
Friday, the threat will slowly diminish during the weekend.

In the storm term, model upper air analysis indicates that weak
disturbances will attempt to ride over the ridge on Friday. Once
this occurs, the flow aloft becomes more southwesterly and begins
to lose the monsoonal flow component. Therefore, dry air will
start to surge into the region from the west while the center of
the high pressure area remains near the four corners. While the
threat of convective activity will lessen, the heat will continue
until a stronger onshore flow develops. Models show the high
retrograding toward Southern California during the weekend.
Placing the high over California will lead to more heat. This
scenario warranted the issuance of an excessive heat watch as the
potential for a heat warning exist around the Saturday/Sunday time
frame.

By Monday, longer range models solutions indicate the possible
introduction of a stronger trof pattern entering the West Coast.
While models do show some uncertainty in the possible solution,
confidence remains high that a trof could enter the area at the
start of the week. By Tuesday, models place the trof axis more
ashore as the high pressure center moves more toward New
Mexico/Northern Texas. This change in the pattern will lead toward
a cooling trend that may finally break the 100 degree streak.
Afterward, the pattern shows little change as triple digit heat
may not return to the area until after the start of the new month.

&&

.AVIATION...
Areas of MVFR and local mountain obscuring IFR over the Southern
Sierra Nevada from scattered showers and isolated thunderstorms.
Otherwise, VFR conditions will prevail across the central CA
interior for at least the next 24 hours.

&&

.AIR QUALITY ISSUES...
On Thursday July 25 2019... Unhealthy for sensitive groups in
Fresno, Kern and Tulare Counties and Sequoia National Park and
Forest. Further information is available at Valleyair.org

&&

.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...
Flash Flood Watch until 11 PM PDT this evening for CAZ192>199.

Heat Advisory until 8 PM PDT Friday for CAZ179>189.

Excessive Heat Watch from Saturday morning through Sunday
evening for CAZ179>189.

&&

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