Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241135

Area Forecast Discussion
National Weather Service Phoenix AZ
435 AM MST Sat Jun 24 2017

.UPDATE...Updated Aviation and Fire Weather Discussions.



A strong high pressure system will remain over the region producing
more excessive heat on the deserts through Monday. A weakening of
the high pressure system next Tuesday will result in lower afternoon
temperatures next week, mostly near or slightly below the 110 degree
mark. A slight chance of afternoon thunderstorms will return to the
mountains of eastern Arizona Sunday and Monday.



Today and Tonight...

00Z Sat weather balloon soundings highlighted the plume of boundary
layer moisture, mainly below 4000 feet, that seeped north through
the Colorado River Valley the past few days then curved toward
Phoenix. Yet despite this moisture increase, the flow aloft at and
above 300 mb was highly anti-cyclonic and very stable. Ditto for
Saturday afternoon and evening over our forecast area, southeast CA
to south central AZ. And for the most part, the lower Colorado River
Valley moisture seepage is over.

However, significant boundary layer moisture from west Texas is
expected to push to the eastern AZ border today. New Mexico easterly
winds are remnants of a back door cold front that pushed into
northeast New Mexico/Texas panhandle from Nebraska/Kansas Friday
afternoon. Models forecast a few late day thunderstorms over the
higher terrain of the White Mountains which should stay east of our
southern Gila County zone.

The Excessive Heat Warning continues today as desert temperatures
rebound into the 115-117 degree range.

Sunday and Monday...

Significant boundary layer moisture from New Mexico will continue to
push deeper into southeast AZ Saturday night and Sunday. At the same
time, models continue to forecast a weak Pacific disturbance at and
above the 300 mb level to move from offshore San Diego into
southeast AZ by Sunday evening. A better chance of late afternoon
and evening thunderstorms are forecast over parts of southeast AZ
and the White Mountains, and close enough to mention a threat of
thunderstorms over the higher terrain of our southern Gila County
zone. Could convective outflows from southeast AZ move toward the
Phoenix area for gusty winds, blowing dust, and a spike in humidity
Sunday evening. This question will be better answered perhaps Sunday
afternoon as we see the character, coverage, and behavior of these
predicted storms in southeast AZ.

Following the Sunday evening upper level disturbance in southern AZ,
a more anti-cyclonic flow regime at and above 300 mb will likely
stabilize the atmosphere over our forecast area Monday despite a
moisture increase. Upper level deformation is still seen in the
models  over far southeast AZ/northwest Mexico for a continuation of
afternoon/evening storms. Otherwise partly cloudy skies and dry
weather will cover our forecast area Monday, with the exception of a
slight chance of thunderstorms over the higher terrain of southern
Gila County bordering the White Mountains.

Tuesday through Friday...

Somewhat stable northwesterly flow aloft at and above 300 mb level
will develop over most of AZ.  At the same time drier 850/700 mb
winds veer from the west to thin the boundary layer moisture in our
forecast area. This should preclude any thunderstorm developments in
our area of responsibility

High temperatures are forecast edge lower this period as the center
of the high pressure system and thicker atmosphere move south into
northwest Mexico.


South-Central Arizona including KPHX, KIWA, and KSDL:

Light easterly winds this morning will change over to the west
during the early afternoon at 8-10kt with a few occasional wind gusts of
15-18kt from mid afternoon to early evening. Expect partly cloudy
skies with BKN to occasionally SCT mid clouds near 18kft. Winds will
become southeasterly late tonight at 7-8kt.

Southeast California/Southwest Arizona including KIPL and KBLH:

Light and variable winds through early afternoon will begin to favor
the south and southwest starting mid afternoon through this evening
at 8-10kt, with a few gusts of 15-18kt possible. Expect partly
cloudy to mostly clear skies with FEW-SCT mid to high clouds near 16-



Monday through Friday:

A high pressure system remaining over the west on Monday with very
hot conditions will gradually be replaced by dry westerly and then
northwesterly flow aloft during the period. Very hot maxTs of 110-
115F on Mon. across the lower deserts will gradually drop each day
until they reach 104-108F by Fri.  With a very slight chance of
isolated PM t-storms in the eastern high country on Mon., dry
lightning fire starts are possible. Min RH`s near 5 percent in far
western deserts, to 15 percent in central deserts on Mon., will fall
to mostly single digits by Wed. Gusty winds, as well as possible
outflow breezes from distant storms to the southeast, with gusts
of 15-22kt, are also expected each afternoon through Wed.
Overnight recoveries will range from poor to fair in most lower
desert locales.



Record highs this week:

Date           Phoenix            Yuma
----           -------            ----
6/23         116 in 1974        116 in 1959
6/24         118 in 1929        120 in 1957
6/25         120 in 1990        119 in 1994
6/26         122 in 1990        122 in 1990


Spotters should follow standard reporting procedures.


AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ530-533-534-

     Excessive Heat Warning until 9 PM MST /9 PM PDT/ Sunday for

     Heat Advisory until 9 PM MST Sunday for AZZ557-558-563.

CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ560-561-563-

     Excessive Heat Warning until 9 PM PDT Sunday for CAZ562-564-565.



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