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Area Forecast Discussion (AFD)

Issued by San Joaquin Valley, CA (HNX)

FXUS66 KHNX 161037

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
337 AM PDT Thu Aug 16 2018

Chance of afternoon thunderstorms in the high Sierra and Mojave
desert through Thursday. High pressure will build over central CA
bringing a warm and dry trend for the weekend.


A brief reprieve from the heat was observed on Wednesday as many
San Joaquin Valley locations reports max temperatures below 100
degrees. This minor cooling was the results of having the marine 
layer rise above 2000 feet MSL -- as observed on the Fort Ord 
Profiler. While most of the San Joaquin Valley still saw max 
temperatures reaching into the 90s, the Century mark was kept 
mostly to the Kern County Deserts. Yet, after having the marine 
layer reach above 2000 feet MSL, the trend is to now have the  
marine layer start dropping in height this morning -- which will 
turn off the cooling across the area. However, the marine air 
that is currently over the region will need to modify before the 
heating starts again. Therefore, will see one more day of max 
temperatures below 100 degrees before the century mark is observed
again over the San Joaquin Valley closer to the weekend.
Furthermore, an area of weakness allowed the air flow aloft to
turn in a more southeasterly direction. Observed and model
precip-water analysis is showing a northward surge of moisture
that will increase the convective potential over a larger portion
of the eastern side of the Central California Interior. 

The eastern side is mostly the Sierra Nevada Crest and the Kern 
County Mountains and Deserts. While model upper air analysis is
indicating a more westerly turn of the winds aloft toward the end
of the week, a good chance of mountain and desert convection could
exist for this Thursday. Therefore, will continue to mention a
chance of thunderstorms over the Sierra Nevada Crest, the eastern
portion of the Kern County Mountains and the Kern County portion 
of the Mojave Desert. A comparison of precip-water values from 
the Southwest are still showing a slight increasing trend in 
moisture. Therefore, as model analysis indicates a possible 
northward surge of moisture under the southeasterly flow, 
confidence grows for possible convection until the flow become 
more westerly. 

Once the wind flow turns in a more westerly direction toward the 
end of the week, the district will return to a more heat and dry
pattern as a disturbance cross the Pacific Northwest and Northern
California. While the disturbance may be too far north to cool 
down the district, the change in wind direction will shift the 
moisture east and away from the district. Therefore, having a very
strong ridge pattern over the west will force disturbances to take
a more northerly trajectory through the Pacific Northwest and
Canada. Because of the strong ridge, the district will see a
return to warm and dry conditions by the weekend as the heat 
continues into the latter half of August. By the middle of next 
week, models show another weak disturbance pushing through the 
Pacific Northwest and forced to move into the Inter-mountain West
as it has to go around the high pressure ridge to will still sit 
over the west. Therefore, confidence grows that the heat will
indeed continue over the region.


Areas of MVFR visibility in smoke and haze can be expected in the 
foothills and higher elevations of the Sierra during the next 24
hours. A chance of afternoon thunderstorms are possible along the
Sierra crest after 19Z today and 03Z Friday. Otherwise, VFR 
conditions will prevail across much of the central California 
interior during the next 24 hours. 


Please see SFOAQAHNX for an Air Quality Alert

On Thursday August 16 2018... Unhealthy for sensitive groups in
Kern County and Sequoia National Park and Forest.
Further information is available at Valleyair.org



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.


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