267
FXUS65 KPSR 251741
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1041 AM MST Wed Sep 25 2024

.UPDATE...Updated 18Z Aviation Discussion.

&&

.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 region. In fact, temperatures
resembling the middle of June will be more common through early
next week. Dry air will also remain entrenched over the area well
into next week resulting in mostly clear skies and a lack of
rainfall.

&&

.DISCUSSION...
High amplitude ridging has now become positioned from the Desert
Southwest all the way into southern Canada and this ridge will
hardly budge over the next 7 days or so. H5 heights have increased
across the Desert Southwest to between 587-589dm with the high
center positioned near the Four Corners. Temperatures over the
last few days have quickly ramped higher with Phoenix`s highs
rising 18 degrees since Saturday and 16 degrees at Yuma. With the
center of the ridge staying just to our east through Thursday,
temperatures may rise another degree or so from what we saw
yesterday with Phoenix`s chances of reaching 110 degrees at or
just over 50%. On average, we expect highs ranging from 105-110
degrees across the lower deserts for today and Thursday before
getting even hotter Friday and through the weekend. These hot
temperatures are uncharacteristic for this time of year and it
seems highly likely KPHX will break several daily record highs
through the weekend with roughly 20% daily odds of Yuma breaking
records.

Guidance now finally seems to have a good handle of this heat
wave with the worst of the heat likely occurring Friday and
through the weekend as the center of the ridge is forecast to
move over Arizona and strengthen to H5 heights of 590-592dm.
Ensemble guidance shows H5 and H7 temperatures reaching near or
even to record levels during this period over much of Arizona.
Forecast temperatures have risen even further over the weekend
into early next week with highs peaking between 110-113 degrees on
Saturday, or around 15 degrees above normal. This latest NBM run
shows KPHX breaking daily record highs by 5 or 6 degrees on Friday
and Saturday with ~95% probability of breaking the daily record
highs for those days.

Areas of Major HeatRisk are expected across much of the south-
central Arizona lower deserts through Thursday before expanding
over the southwest Arizona and southeast California lower deserts
Friday and Saturday. This blocking ridge is likely to hold a firm
grasp over our region through at least early next week, possibly
longer. The NBM does gradually lower temperatures during the first
half of next week, but it seems too aggressive considering both
the GEFS and EPS keep at least 588-590dm H5 heights over the bulk
of the region. It is very likely forecast temperatures during the
first half of next week will continue to trend upward over the
next several model runs, likely resulting in an eventual extension
in the Excessive Heat Warnings that are currently in place.
Although it is still beyond a week out, guidance does somewhat
agree on an eventual weakening of the ridge later next week. If
this were to happen, we should see highs eventually drop down to
around or even below 105 degrees for daily highs. Looking out
through the end of next week, 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. Ealry 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 conitnue 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

&&

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