Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 201102

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
402 AM PDT Sun Aug 20 2017

.SYNOPSIS...An area of low pressure 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...Some mid level clouds remain over the district from
afternoon convective activity. Otherwise clear skies prevailing
this morning. Temperatures running cooler across the central
valley due to a deeper marine layer along coast. Otherwise little
change elsewhere. Thunderstorms occurred over the Sierra Nevada
and Kern Mountains and expect a repeat of thunderstorm activity
for Sunday afternoon and evening. Conditions remain conditional
unstable with little change in airmass and precipitable water
values up to 120 percent above normal over central CA. Water
vapor imagery show an upper trough off the CA coast developing
Southward. This feature will provide favorable conditions for
continued convective forcing with the afternoon wind convergence
over the mountains.

Models in agreement that the trough will remain off the
CA coast through Tuesday. Another upper disturbance will move
south into the trough retrograding the trough further offshore.
This will maintain an east to southeast mid level flow tapping
into some deeper monsoonal moisture over Arizona and northern
Mexico. Models show the 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 for more widespread showers and
thunderstorms early next week. The GFS models indicate a moderate
E to SE flow Monday night and Tuesday as the low closes off point
conception. This could bring the convective storms into the into
the foothills or the east side and south end of the San Joaquin

The models forecast the trough to weaken as it moves onshore over
S CA Wednesday. A westerly flow aloft should bring drier and
stable conditions Thursday. A warm and dry trend expected
thereafter as an upper level ridge builds northwestward from


Isolated to scattered thunderstorms over mountains after 20z this
afternoon and extending into desert areas after 06z tonight.
Otherwise VFR conditions expected across the central CA interior
during the next 24 hours.


Please see SFOAQAHNX for an Air Quality Alert

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



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

Certainty levels include low...medium...and high. Please visit for additional information
an/or to provide feedback.


.HNX Watches/Warnings/Advisories...


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