Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 202100

Area Forecast Discussion
National Weather Service Hanford CA
200 PM PDT Sat Jul 20 2024

1. An Excessive Heat Warning is in effect for
the Kern County Desert and Mojave Desert Slopes beginning 11 AM
PDT Sunday and in effect for the San Joaquin Valley, Yosemite
Valley, Lake Isabella, and Sierra Nevada foothills beginning 11
AM PDT Monday. Both warnings are in effect through 11 PM PDT

2. The high risk of grass fires in the valley continues, with
enhanced fire behavior even with lower wind speeds. In the
Sierra Nevada, the risk increases with afternoon thunderstorms
possible from today through Thursday.

3. Periods of afternoon thunderstorms in the Sierra Nevada
continue through the weekend and into next week. There is a 10
to 20 percent probability each afternoon.

4. There is a 30 to 60 percent chance for afternoon highs to
reach or exceed 105 degrees in the San Joaquin Valley on Monday,
chances increase to 75 to 95 percent for Tuesday then lower to
55 to 75 percent for Wednesday and Thursday.


Minimal change in the overall weather pattern as temperatures
soar toward the century mark and scattered showers form over the
higher terrain of the Sierra Nevada. Currently, temperature
trend over the pass 24 hours have seen a rise of 1-3 degrees
from Noon-time on Friday. Therefore, will have no problem
reaching the century mark today as the San Joaquin Valley
approaches its next heat-wave next week. As for convection,
Probability of Thunder sits at around 30-40 percent from
Yosemite to Mount Whitney  along the crest (higher terrain)
this afternoon. Based on current satellite and radar imagery,
will expect a chance (near 50 percent) of a showers or
thunderstorm forming just north of the Kern County Mountains
north to Tioga Pass. The axis of the high pressure ridge will
continue to shift westward as Central California is now on the
verge of seeing another excessive heat event before a cool-down
by next weekend.

Hi-Res short-range Ensemble analysis is still showing good
agreement with the solution of shifting the ridge of high
pressure over California toward this weekend. In the meanwhile,
the continued southeasterly flow around the ridge will allow
more monsoonal moisture to surge into the region. While the
shift will take time, mountain showers and thunderstorms
coverage will continue to grow as the ridge axis moves more over
California. Probability of Thunder will remain at the 30-40
percent level, yet, coverage of the percentage will increase
from now through Wednesday. As for temperatures, while
Probability of Exceedance (PoE) of reaching 105 degrees across
the San Joaquin Valley starts out low (15-25 percent) today,
they do grow to 75 to 85 percent with local 90 percent by
Tuesday. Monday will be the wild-card as PoE will range around
50 percent. Therefore, high confidence in the heat-wave event
will be on Tuesday and Wednesday (and possibly Thursday) before
PoE show a drop off around Friday. Current thinking is that
Tuesday and Wednesday will be the dangerous heat days with
Monday and Thursday the intermediate days.

Minor changes of the flow aloft as ensemble cluster analysis may
allow for continued heat and mountain convection through at
least Thursday. Cluster analysis does hint toward a disturbance
moving into the Pacific Northwest near the Friday time frame.
Ensemble PoE by Friday of reaching 105 degrees drops to near 50
percent. While the ensemble mean is still showing max
temperatures reaching 100 degrees, cluster analysis continues
its downward trend in temperatures and may even go below 100
degrees by next weekend.


Areas of MVFR and local mountain obscuring IFR in showers and
thunderstorms over higher elevations of the Sierra Nevada until
03Z Sun. Areas of MVFR and local IFR visibility will continue in
and around wildfires. Otherwise, VFR conditions will prevail
across the central CA interior over the next 24 hours.





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 for additional information
and/or to provide feedback.


Excessive Heat Warning from 11 AM Sunday to 11 PM PDT
Wednesday for CAZ337>339.
Excessive Heat Warning from 11 AM Monday to 11 PM PDT
Wednesday for CAZ300>321-324-325-332.