043
FXUS65 KPSR 261555
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
855 AM MST Thu Sep 26 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
An unseasonably strong high pressure system will remain planted
across the region into next week bringing excessive heat to much of
the area through at least the weekend. High temperatures are
forecast to reach 110 degrees or higher over a good portion of the
lower deserts through the weekend with Phoenix expected to break
daily records over the next several days. Dry air and mostly clear
skies will also remain entrenched across the region well into next
week.

&&

.DISCUSSION...
Temperatures over the next week or so will resemble more than that
of mid June with long range guidance not suggesting much in the way
of a break any time soon. The unseasonably strong high pressure
ridge has now overtaken much of the Southwestern U.S. into the
Central Plains with the high center over New Mexico. H5 heights over
the Desert Southwest have risen to between 587-589dm with heights
expected to rise to 590-592dm for Friday and Saturday as the high
center shifts westward to over Arizona. The blocking pattern will
strengthen at the same time as the northern jet stream becomes
completely decoupled from the southern jet branch, further cementing
the high pressure ridge over the southern tier states into at least
early next week.

Anomalously high temperatures are forecast into next week with lower
desert highs near or even a few degrees above 110 each day with
readings likely peaking on Friday and Saturday. Saturday`s NBM
forecast highs show readings between 110-114 degrees across all of
the lower deserts, or around 15 degrees above normal. For a while
earlier this week, ensemble guidance had hinted at a possible
disruption and a likely weakening of the high pressure ridge by
early next week, but that is now looking less likely. This was
mostly due to a weak cut-off low situated to our southwest moving
into our near southern California, but this feature now looks weaker
and likely will not bring us much relief. The latest ensemble
guidance does show this low nearing the region this weekend, but
then retrograding back to the west as another high pressure system
tracks eastward toward central and northern California. The NBM
temperature guidance continues to play catch up with each new run in
the latter half of the time range, so we fully expect forecast highs
for much of next week to continue to creep upward. It would not be
surprising to see highs stay near 110 degrees through much of next
week as ensemble guidance has been trending toward H5 heights
staying around 588-590dm into the latter half of next week. If this
were to occur, we could see record or near record temperatures
persisting well into next week. The Excessive Heat Warning currently
goes through Sunday for a good portion of the lower deserts, but we
fully expect to extend it soon through at least early next week for
much if not all of the current Warning area.

&&

.AVIATION...Updated at 1555Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Friday afternoon under
mostly clear skies. Similar to the past several days, light east
winds will persist through much of the afternoon, however a
confidence is good that a westerly switch will occur slightly
earlier than the yesterday, but still later then usual.


Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Friday afternoon under clear
skies. Winds will favor a W/NW component through the period with
extended periods of variability and nearly calm conditions.

&&

.FIRE WEATHER...
A blocking weather pattern will keep an unseasonably strong high
pressure system over the region into next week. This will result in
well above normal temperatures each day and continued dry
conditions. High temperatures are expected to reach 10-15 degrees
above normal through at least the weekend with record temperatures
likely for many locations, especially across the eastern districts.
Daily MinRHs of around 10% can be expected across the lower deserts
to around 15% over higher terrain areas. Winds will remain fairly
light generally following diurnal wind patterns with the exception
of some breezier conditions on Saturday.

&&

.CLIMATE...

Record highs this week:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
Sep 26    108 in 1989    111 in 2010    110 in 2010
Sep 27    107 in 2009    111 in 1963    111 in 2009
Sep 28    108 in 1992    108 in 1994    109 in 2009
Sep 29    107 in 2003    110 in 1980    110 in 1969
Sep 30    107 in 2010    109 in 2020    108 in 2020
Oct 1     107 in 2020    110 in 1980    110 in 1980

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM this morning to 8 PM MST
     Sunday for AZZ530-533-534.

     Excessive Heat Warning until 8 PM MST Sunday for AZZ537>544-546-
     548>551-553>555-559.

     Excessive Heat Warning from 10 AM Friday to 8 PM MST Saturday
     for AZZ531-532-535-536.

CA...Excessive Heat Warning from 10 AM this morning to 8 PM PDT
     Sunday for CAZ569.

     Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday
     for CAZ566-567-570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman
CLIMATE...18