754
FXUS65 KPSR 152132
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
232 PM MST Sat Jun 15 2024

.SYNOPSIS...
Dry, westerly flow aloft will continue to promote well above normal
temperatures across the Desert Southwest through this weekend. An
Excessive Heat Warning remains in effect for southcentral AZ through
Sunday evening. Slightly cooler temperatures and breezy conditions
will arrive early next week as a trough of low pressure passes
through the Intermountain West. Ridging aloft will then build back
over the region by the latter half of next week, resulting in a
return of very hot temperatures.

&&

.DISCUSSION...
Latest IR WV imagery depicts a ridge of high pressure centered
over N MX while a large scale trough is located over the Pacific
NW. Our forecast area is situated between both of these features
with dry zonal flow aloft prevailing across AZ and southeast CA.
The temperature at Sky Harbor has already surpassed 100 degrees
before 11 AM MST and readings are expected to top out around
110-113 degrees in the Phoenix Metro area this afternoon. Highs
will be equally as hot across southwest AZ and southeast CA today,
reaching 110+F. An Excessive Heat Warning remains in effect today
for much of the lower deserts as well as Sunday for southcentral
AZ. The afomentioned trough will begin to move into the
Intermountain West by Sunday afternoon, allowing heights aloft to
begin to lower, especially across the western half of the region.
Despite a few degrees of cooling yielding a moderate HeatRisk, it
will still be very hot in the Phoenix Metro area Sunday afternoon
where temperatures are expected to peak around 107F-111F. Therefore,
we will leave the Excessive Heat Warning unchanged for now.

As longwave troughing expands across the western CONUS early next
week, 500 mb hghts will continue to fall to near climatological
levels. Temperatures from Monday through Wednesday will still be
around 1-3 degrees above normal in Phoenix, but overnight lows will
be near to slightly below normal mainly in the mid 70s. An
increasing hght gradient and 700-500 mb jet over the region will
result in breezy to locally windy conditions across southcentral AZ
on Monday where gusts could reach 20-30 mph. Higher gusts up to 30-
35 mph will be possible over the higher terrain areas north and east
of Phoenix resulting in near critical fire weather concerns on
Monday afternoon (see fire weather disco for more details).

Heading into the latter half of next week, we will see the return of
an unseasonably strong ridge of high pressure that will set up over
the Desert Southwest. Ensemble and deterministic H5 heights are
forecast to rise above 590 dam by next weekend. There are still some
differences between the EPS and GEFS regarding the strength of the
ridge, but the NBM is still showing highs rising above 110 degrees
at many lower desert communities as early as next Thursday. The NBM
is still indicating the hottest day will be Friday with readings
between 111-116 degrees in the Phoenix Metro.

There are still signals in the global ensembles that we will see a
push of low level moisture into the eastern half of AZ by next
weekend. NBM Guidance has been consistent in showing isolated
thunderstorms (10-30% chances) beginning as early as Thursday across
the higher terrain of southcentral and southeastern AZ. For now the
chances for rain in central deserts are below 10%, but this could
change depending on the evolution of the high pressure system next
weekend into the following week. Either way this would be the first
signs of our monsoonal pattern beginning to awaken.

&&

.AVIATION...Updated at 1755Z.

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

No major aviation weather concerns will exist through the TAF
period under clear skies. After a period of southerly variability
for the next several hours, winds will establish out of the SW/W
this afternoon. Occasional late afternoon/early evening gusts to
between 15-20 kt can be anticipated, with elevated west winds
lasting later into the evening than yesterday before eventually
shifting E-SE overnight. During the mid to late morning hours
tomorrow, winds will begin to veer out of the south, potentially
leading to a period with a southerly cross-runway component at
KPHX and KDVT before establishing out of the SW early tomorrow
afternoon. Wind speeds are expected to be stronger tomorrow, with
afternoon/early evening gusts to around 20 kts across all the
terminals.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns will exist through the next 24 hours
under clear skies. Winds will favor SE/S at KIPL today and early
tomorrow and are expected to shift SW/W this evening into the
overnight hours. Evening gusts to between 20-25 kt are likely at
KIPL. Winds will favor southerly to southwesterly directions
through the TAF period at KBLH, with afternoon gusts into the low
20s and sustained speeds in the mid teens lasting through the
evening.

&&

.FIRE WEATHER...
Hot, dry, and breezy conditions are progged to develop across
southcentral AZ both Sunday and Monday. This will lead to pockets
of elevated to near critical fire weather. Winds are expected to
increase across the region with gusts reaching 20-30 mph on Sunday
and Monday. The higher terrain areas in southcentral AZ are
likely to see the strongest winds on Monday with gusts as highs as
30-35 mph possible, resulting in localized critical fire weather
conditions. Minimum afternoon humidity levels will continue to
remain 10% or less through Monday following poor overnight
recovery of only 15-30%. Humidity levels will improve modestly to
10-15% range Tuesday and Wednesday before falling back to 5-10%
later next week. Strong high pressure should build back over the
districts during the latter half of next week resulting in warming
temperatures, but also weakening winds. There are a few models
suggesting somewhat better moisture sneaking into eastern Arizona
beyond next weekend yielding a few thunderstorms over mountain
areas, yet confidence is very low given any early season activity
typically results in little actual wetting rainfall.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ534-537>555-
     559-560-562.

CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ562-
     563-566-567-570.

&&

$$

DISCUSSION...Salerno
AVIATION...Whittock
FIRE WEATHER...Salerno/Kuhlman