Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 202340 AAA
AFDHNX

Area Forecast Discussion
National Weather Service Hanford CA
440 PM PDT Tue Oct 20 2020

...Update to Air Quality Issues Section...

.SYNOPSIS...
High temperatures Wednesday afternoon will continue to be well
above normal for this time of year. A cooling trend is expected
Thursday through Sunday. By Sunday afternoon, maximum temperatures
should be five to ten degrees below their typical values for the
latter half of October. Dry weather will persist through at least
Saturday.

&&

.DISCUSSION...
Above normal temperatures and dry conditions will continue over
the region for a couple more days before we begin a strong cooling
trend. Low daytime humidity and poor overnight recovery will
also continue through Thursday before we start seeing some
increased humidity.

The cooling trend and increasing humidity will be the result of a
strong low pressure trough across Canada and the northern tier of
the US. Models have been having a hard time handling this trough
will some being more progressive and keeping to our north with
cooler by dry conditions. Other models dig the trough back into
California and bring at least some chance of precipitation. The
12Z deterministic GFS has continued its trend of keeping us dry,
while the ECM has flipped from its 00Z run and now tries to bring
in some light precipitation. The NBM continues to be in between
and looking the ensembles, it seems the reasonable way to go for
now. The NBM keeps just a slight chance of showers over the
Sierra, with measurable rain mainly near Yosemite and possibly the
highest elevations of the Sierra on Sunday. Another possibility
is that the trough splits and takes a much weaker low off the
coast which could bring a slight chance of precipitation into the
LA area and possibly brushing the mountains of Kern County over
the weekend.

The biggest effect from this system will be to bring cooler
temperatures to the region. The cool down will begin Thursday and
continue through Sunday. We will go from having temperatures 5-15
degrees above normal on Wednesday to having temperatures 5-10
degrees below normal by Sunday afternoon. Humidity values will
gradually increase in the mountain through this period giving some
relief from the very dry conditions we have seen over the on-
going fires. Unfortunately, it does not look like there will be
enough rain or snow showers to make much of a difference on the
area fires. Confidence continues to be low with the precip
forecast, but medium to high for the cooldown for the weekend.



&&


.AVIATION...
MVFR visibilities due to smoke and haze are possible in the San
Joaquin Valley tonight. VFR conditions will prevail in the San
Joaquin Valley Wednesday. IFR visibilities due to smoke and haze
are likely in the Sierra Nevada through at least the next 24
hours.

&&

.AIR QUALITY ISSUES...
Please see SFOAQAHNX for an Air Quality Alerts.

On Wednesday, October 21st, 2020, unhealthy for sensitive groups in
Kern County.

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 low.

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...
None.
&&

$$

public...Bean
aviation....Bean

weather.gov/hanford



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