Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
FXUS66 KHNX 282035
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
135 PM PDT THU JUL 28 2016
A ridge of high pressure continue to bring hot temperatures through
the weekend. Afternoon and early evening showers and thunderstorms
are possible along the Sierra crest today and through the weekend
and will possibly spread into the Kern County mountains and desert
by the weekend.
.DISCUSSION...The big weather story across the central California
interior continues to be the heat. Even though it will abate
somewhat by early next week, high temperatures will still reach
the century mark throughout the San Joaquin Valley, lower
foothills and the Kern County desert for at least the next 7 days.
No doubt this will be the longest stretch of triple digit heat so
far this year in the San Joaquin Valley. The last time we had a
spell of triple digit heat this long was in the summer of 2013.
Bakersfield tallied 13 consecutive days of 100+ heat that year
while Fresno endured a 19-day stretch. Blame our current hot spell
on a strong upper level ridge of high pressure that has been parked
over the Great Basin since Monday.
In addition to the heat, the airmass residing over central California
has become stagnant. Smoke aloft from the Soberanes wildfire in
Monterey County has become trapped underneath the upper level ridge
where it will likely remain for many more days. Several pilot reports
indicate that this layer of smoke is between 5500 feet and 7500 feet.
This is certainly a health concern for residents of the San Joaquin
Valley, especially those with respiratory ailments. Consequently,
the San Joaquin Valley Air Pollution Control District has issued an
Air Quality Alert for the entire valley. (For details, please see the
As we look at the broader synoptic picture, the models agree in
keeping the upper level ridge of high pressure firmly entrenched over
the Great Basin during the next 3 to 5 days. Meanwhile, easterly waves
will traverse central Mexico and exit into the Eastern Pacific, which,
so far has proven to be a very active season. Although some of this
tropical moisture will work its way up into central California during
the next 72 hours, the high pressure ridge at our latitude will suppress
the deepest moisture well to our south. Some of this higher based
tropical moisture showed up Wednesday and now that it is here, it will
undoubtedly linger through at least Sunday and aid in the development
of isolated afternoon and evening thunderstorms near the Sierra crest.
Most of these thunderstorms will bring little if any measurable rain,
so dry lightning and gusty, erratic winds associated with them will be
the biggest threat to existing and possibly new fires over the Sierra.
A few of the models forecast a slight increase in tropical moisture
across central California this weekend, so in addition to the Sierra
crest, the Kern County mountains and desert will also face a slight
chance of afternoon and evening thunderstorms Saturday and Sunday.
After this weekend, the GFS model hints of a subtle change in the
upper air pattern...one that weakens the ridge and forecasts a slightly
drier southwesterly flow across central California early next week.
If the GFS ends up being right, then tropical moisture aloft will be
pushed out of central California by late Monday and end the threat of
afternoon thunderstorms over the mountains and desert. The majority of
the models, however, keep the upper level ridge anchored over central
California through next Thursday. If so, there will be little if any
airmass change over the CWA for the next 7 days. If you can picture
this high pressure ridge as a tall mountain of very warm air, you get
the idea of how difficult it is to move it out of the way. In truth,
it would take a fairly strong upper level eastern Pacific trough to
kick this ridge out of the Great Basin. The ensembles suggest this
will not happen until maybe the 10th of August.
Cumulus buildups and isolated thunderstorms are expected over the
Sierra Nevada this afternoon and evening, otherwise VFR conditions
can be expected through Central California for at least the next 24
.AIR QUALITY ISSUES...
The San Joaquin Valley Air Pollution Control District has issued an
Air Quality Alert due to smoke impacts in San Joaquin, Stanislaus,
Merced, Madera, Fresno, Kings, Tulare, and the Valley Portion of Kern
Counties from the Soberanes Fire. For details, please refer to the
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.