Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 192349 AAA
AFDHNX

Area Forecast Discussion...UPDATED
National Weather Service San Joaquin Valley - Hanford CA
449 PM PDT Sat Aug 19 2017

...UPDATED AIR QUALITY SECTION...

.SYNOPSIS...A weak upper level storm system will remain
anchored off the southern California coast through Tuesday and
bring a chance of mainly afternoon showers and thunderstorms to
the Sierra. The threat of thunderstorms will extend into the Kern
county mountains and desert and the Sierra foothills by early next
week with the arrival of monsoonal moisture.

&&

.DISCUSSION...Convection is firing up over the high Sierra again
this afternoon and, like yesterday, the heaviest thunderstorms are
impacting Yosemite National Park and the highest elevations of
the Sierra north of Kings Canyon. During the remaining hours of
the afternoon, thunderstorms will continue to pop up over the
mountains, including the Tehachapi`s. The maturest thunderstorms
will bring briefly heavy rain, hail, frequent lightning and gusty,
erratic winds. With little change in the overall pattern forecast
through the weekend, we can expect a repeat occurrence of
thunderstorm activity over the mountains Sunday afternoon into
Sunday evening.

Otherwise, an east to southeast flow aloft will prevail over
the central California interior for at least the next 48 hours
while a weak upper level low remains anchored near Point
Conception. With time, this system will eventually tap into some
deeper monsoonal moisture over Arizona and northern Mexico. The
models, in particular the GFS, have backed off a bit on the
westward extent of this moisture but most agree that this
moisture will begin to infiltrate the Kern county mountains and
desert by late Sunday night and advect northward up the Sierra
during the day Monday. This area will become the primary focus of
more numerous showers and thunderstorms early next week. However,
it won`t take much of a westward shift to bring the threat of
thunderstorms into the foothills or the east side and south end of
the San Joaquin Valley. This is something will have to closely
monitor from late Sunday night through Tuesday evening. At the
very least, the valley and foothills will receive debris clouds
from dissipating mountain thunderstorms each of the next few
evenings/nights.

During midweek, the models forecast the remnants of this weak
upper level low to finally move inland into southern California.
Whether this low gets picked up or absorbed into an upper level
trough that approaches the Pacific Northwest coast is still
uncertain since the models differ on what actually becomes of
this feature. Whatever the case, winds aloft should become
westerly by Wednesday night and hence bring a slightly drier and
more stable air mass into the CWA. Wednesday will probably be the
last day of afternoon thunderstorms, most of which will be
confined to the very highest elevations of the Sierra.

In the 5 to 7 day period, the models agree in building an upper
level ridge of high pressure northwestward from Texas. Once
over California, this ridge is progged to amplify next weekend
which will surely bring a return of widespread triple digit heat
to the San Joaquin Valley, lower foothills and the Kern county
desert. Up until then, maximum temperatures each day will
generally remain below the century mark in these areas. If a
sufficient amount of monsoonal moisture advects into the central
California interior early in the week, skies will be a little
cloudier. Clouds could interfere with a view of the solar eclipse
Monday morning in addition to keeping max temperatures slightly
below normal. On the other hand, their presence will keep low
temperatures a bit warmer than normal Sunday night and Monday
night. Otherwise, we should expect a rather humid weather
regime to hang on through the early part of next week.

&&

.AVIATION...Isolated to scattered afternoon thunderstorms over
mountains from 20z to 04z. Otherwise VFR conditions expected
across the central CA interior during the next 24 hours.

&&

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

The San Joaquin Valley Air Pollution Control District in addition
to the Mariposa County Air Pollution Control District have issued
Air Quality Alerts due to smoke impacts from wildfires over the
Sierra, in particular the South Fork Wildfire.

For details, please see the SFOAQAHNX.

On Sunday August 20 2017... Unhealthy for sensitive groups in
Fresno... Kern... Kings 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.php for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...NONE.

&&

$$

public...Durfee
avn/fw...Bean
synopsis...Durfee

weather.gov/hanford



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