142
FXUS65 KPSR 261004
AFDPSR

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

.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 0540Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns will exist through the TAF
period under FEW mid level clouds late this evening, distant
cumulus over the AZ high terrain tomorrow afternoon, and otherwise
clear skies. Southwest winds at KPHX and KIWA will shift southeast
within the next several hours. Expect a typical westerly shift
tomorrow afternoon around 21-22Z across the terminals. Speeds are
expected to remain mostly aob 7 kt.

Southeast California/Southwest Arizona including KIPL and KBLH:
Extended periods of light winds (aob 5 kt) and variability will be
common at both terminals, under clear skies. However, winds at
KIPL will continue to favor west through the overnight hours
before becoming variable tomorrow morning. By tomorrow evening,
winds at both terminals are expected to favor W/NW.

&&

.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...Whittock
FIRE WEATHER...Kuhlman
CLIMATE...18