659
FXUS65 KPSR 252005
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
105 PM MST Wed Sep 25 2024

.SYNOPSIS...
An unseasonably strong high pressure system building over the
region will strengthen through the weekend bringing a return of
excessive heat to much of the area. In fact, temperatures resembling
the middle of June will be more common through early next week. Dry
air will also remain entrenched well into next week resulting in
mostly clear skies and a lack of rainfall.

&&

.DISCUSSION...
High amplitude ridging has now become established from the SW Conus
into southern Canada with a blocking pattern across the southern
tier of states ensuring this feature will move little through at
least the middle of next week. Objective analysis depicts H5 heights
very near 588dm early this afternoon with the high pressure center
over southern Colorado. As a shortwave and jet energy lifts from the
Pacific NW over the ridge axis into southern Canada in the next 48
hours, models are in excellent agreement depicting modest
retrogression and strengthening of the positive H5 anomaly upwards
of 592-594dm with the anti-cyclone center settling directly over the
CWA. Correspondingly, ensemble guidance remains resolute showing H8-
H7 temperatures reaching at or above the 99th percentile leading to
surface readings at or above daily records. Numerical guidance
remains very narrow advertising high temperatures 8F-15F above
normal through the remainder of the week with the most anomalous
heat occurring Friday and Saturday. Undoubtedly, a prolonged string
of records will be broken at Phoenix Sky Harbor including the latest
110F in the period of record, with more scattered daily records in
Yuma given the higher record thresholds.

With a zonal northern stream jet retreated into southern Canada and
a continuation of blocked southern Conus flow, little will change in
the synoptic pattern through the first half of next week. A majority
of ensemble members indicate H5 heights at or above 590dm being
maintained over the forecast area with little impetus available to
budge this anti-cyclone. The official NBM forecast continues to play
catch-up to match the synoptic pattern with each successive run
prolonging the excessive heat temporally. Thus, even though the
official forecast depicts slightly lower temperatures during the
first part of the week, it is very likely forecasts will continue to
trend upward the next several model runs likely resulting in an
eventual extension in the Excessive Heat warnings. Already in the
latest model output, more expansive areas of major HeatRisk are
evident through Tuesday and an extension in time and space will
probably be realized within the next 24 hours. There is some
ensemble support that Pacific energy will partially dislodge or
dampen the subtropical ridge during the middle and latter half of
next week finally bringing an end to the excessive threshold, but
possibly not relieving the region from above normal temperatures.
Nevertheless, there is no indications of increased moisture over the
next 7-10 days and rain chances should continue to stay near 0%.

&&

.AVIATION...Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Easterly winds, with speeds aob 8 kt, will continue before becoming
more southeasterly early this afternoon. Early this evening winds
may favor more of a northwesterly component before going westerly
for a few hours this evening. Winds will be light and variable at
times, especially around wind shifts. Winds will then go back
easterly during the overnight hours. Skies will be mostly clear with
FEW-SCT clouds with bases around 12-14 kft.


Southeast California/Southwest Arizona including KIPL and KBLH:
Extended periods of light and variable winds will continue at both
terminals. A period of light southwesterly winds is expected at KIPL
this evening and during the overnight hours. At KBLH, a period of
light southerly/southwesterly winds is expected this evening and
during the overnight hours. Clear skies will persist.

&&

.FIRE WEATHER...
Strong high pressure will persist over the region through at
least the weekend resulting in well above normal temperatures and
continued dry conditions. Lower desert highs temperatures are
likely to reach 10-13 degrees above normal starting today and
through the weekend. MinRHs will continue to dip down to around
10% over the lower deserts to 15-20% over higher terrain areas
through the rest of the week, while winds remain light generally
following diurnal wind patterns.

&&

.CLIMATE...

Record highs this week:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
Sep 25    108 in 1989    112 in 1963    110 in 2015
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 2012    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 Thursday to 8 PM MST Saturday
     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 Thursday to 8 PM PDT Saturday
     for CAZ569.

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

&&

$$

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