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FXUS66 KHNX 130158 AAA

Area Forecast Discussion...UPDATED
National Weather Service San Joaquin Valley - Hanford CA
558 PM PST Tue Dec 12 2017

Updated Air Quality Issues section.


High pressure will remain over the region for the next several
days with continued dry weather. 


Very dry easterly flow aloft continues this afternoon as the rex 
block pattern of high pressure to the north and low pressure to 
the south of the Central California Interior continues. Many many 
consecutive hours of single digit relative humidity values are
occurring in the Sierra and the Kern County Mountains where the 
dry air can move in from the east. This has prompted the issuance
of a Red Flag Warning through Wednesday evening. 

With the calender saying mid December, the long nights. dry air  
and clear skies are allowing for a continuation of cold overnight
temperatures at most lower elevation locations and this trend will
continue for the next several days. High pressure aloft has really
locked in an inversion at elevations ranging from 4500 to around
7500 feet over the entire area and below this inversion there is
very little mixing of air. Over the San Joaquin Valley, terrain is
trapping the airmass and daily increases in particulate matter
will cause increasingly dirtier air which may allow for additional
fog formation tonight and early Wednesday. 

Forecast models keep the ridge in place over the region for the
next several days, and shunt any incoming Pacific weather systems
well to the north. Once weak system is progged to move across 
Oregon and into the Great Basin on Friday night, however the only
affect over the forecast area may be some high clouds and
hopefully a little better nighttime humidity recover over the
mountains by the end of the week.  

Through Tuesday of next week, forecast models continue to hold the
ridge in place for dry weather. After Tuesday, the latest ECMWF 
model develops and drives a deep, closed low off the west coast ,
which is a change from the previous run. The GFS is also dropping
a trough down into the region, but keeps it inland. This could be
the beginning of a shift in the longwave pattern way out around
Friday of next week. Model accuracy gets RATHER LIMITED this far 
into the future, therefore as of today this forecaster is not 
putting too much confidence in this change in the pattern. The 
pattern will undoubtedly change sometime and maybe for only for a 
short time. As of this morning a wait and see approach seems to be
the most reasonable way to proceed.


Widespread MVFR visibility in haze and mist will persist in the San 
Joaquin Valley, with areas of IFR and local LIFR/VLIFR in fog 
developing until 18Z Tuesday. Otherwise, VFR conditions will prevail 
over the central CA interior during the next 24 hours. 


On Wednesday December 13 2017...Unhealthy for sensitive groups in
Kern...Kings and Tulare Counties. Fireplace/Wood Stove Burning 
Status is: No Burning Unless Registered in Fresno...Kern...Kings...
Madera...Merced and Tulare Counties. Further information is 
available at



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
an/or to provide feedback.


.HNX Watches/Warnings/Advisories...
Red Flag Warning until 8 PM PST Wednesday CAZ295>297.



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