977
FXUS65 KPSR 052321
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
421 PM MST Sat Oct 5 2024

.UPDATE...Updated 00z Aviation Discussion...

&&

.SYNOPSIS...
Record-breaking heat will continue through at least Monday, with
very little day-to-day changes in the weather pattern. An Excessive
Heat Warning remains in effect through Monday as afternoon high
temperatures reach upwards of 15 degrees above normal. A slight
downtrend in temperatures is expected by the middle to end of next
week as a weak disturbance moves in from the west, but temperatures
will continue to remain above normal.

&&

.DISCUSSION...
A hot, dry weekend is underway as a strong ridge of high pressure
over the southwest CONUS continues to promote record-breaking
excessive heat. As of noon, Phoenix Sky Harbor has reached 106
degrees, which breaks the daily record high and now brings Phoenix
up to 12 consecutive days of temperatures tying or breaking daily
record highs. In addition to the record highs, Phoenix has now had
8 consecutive days of record warm lows. Record-breaking
temperatures will continue through at least Monday as temperatures
climb upwards of ~15 degrees above normal. Anyone with weekend
plans should take the necessary heat safety measures to protect
against the heat.

The ridge of high pressure over the Desert Southwest has
strengthened with RAP analysis showing 500 mb heights upwards of 592-
593 dm over the region. As a result, temperatures for many lower
desert locales will top out around 110 degrees through Monday, which
will shatter daily record highs across our area. Temperatures of
this magnitude for this time of year will continue to promote
widespread Major to areas of Extreme HeatRisk and thus an Excessive
Heat Warning remains in effect for much of the lower deserts through
Monday evening. For some context in regards to just how abnormal it
is to see temperatures of this magnitude in October, the record
latest 110 degree temperature occurrence in Phoenix prior to this
year was September 19, 2010, while the average (1991-2020) last 110
degree temperature occurrence is August 26th. Meanwhile, the average
last 100 degree temperature occurrence is today, October 5th.
Temperatures early next week will gradually trend downward, though
the NBM keeps temperatures hot enough into Tuesday to support some
continued areas of Major HeatRisk. Thus, the Excessive Heat Warning
could be extended through Tuesday for parts of the area in future
forecast updates.

A weak shortwave trough will approach the southern coast of
California going into the middle part of next week, leading to
gradual weak height falls over the region. Additionally, the weak
disturbance will also import some mid and upper level moisture,
which could be enough to promote shower development across parts of
the Arizona high terrain but otherwise will lead to an increase in
cloud cover over the region. Temperatures will respond to the weak
shortwave by gradually trending downward during the mid to latter
part of next week, though still remaining well above seasonal
normals as forecast highs remain in the 100-105 degrees for most
lower desert areas. Uncertainty increases heading into next weekend
as guidance suggest a deeper eastern Pacific trough will propagate
into the western CONUS. At this point in the forecast, it`s no
surprise to see a lot of uncertainty showing up in the global
ensemble clusters in regards to the evolution of this trough.
Something to watch as a deeper trough solution into the western
CONUS could finally push temperatures down below 100 degrees for
our area.

&&

.AVIATION...Updated at 2315Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under mostly clear skies can be
expected through the TAF period. Overall wind pattern will
continue to exhibit the typical diurnal tendencies with light
speeds under 7 kts. There will likely be extended periods of very
light/calm and variable winds, especially during the periods of
diurnal transition.

&&

.FIRE WEATHER...
Dry and abnormally hot conditions will persist through early next
week, with lower desert highs ranging between 104-112 each
afternoon. There will be little to no day-to-day change in the
weather through Monday with the continued heat, mostly clear skies,
and light winds. MinRH values will range between 5-15% each
afternoon, while MaxRH readings are expected to be between 20-35%,
with locally higher values in Yuma and Imperial Counties. There will
be a very slight increase in moisture beginning around Tuesday that
may keep MinRH values from falling into the single digits, but most
areas will still see 10-15% readings in the afternoon through the
end of next week. There will also be potential for some regional
rain showers with the moisture increase, but at this time the
chances are very low (5% or less) across the lower deserts and CWR
is near zero. Winds will follow familiar diurnal trends, with
occasional afternoon gusts near 15-25 mph.

&&

.CLIMATE...

Record highs through next Wednesday:

Date        Phoenix         Yuma         El Centro
----        -------         ----         ---------
Oct 5     105 in 2020    108 in 1917    106 in 2020
Oct 6     105 in 1917    108 in 1980    106 in 1964
Oct 7     104 in 1991    108 in 1987    105 in 1991
Oct 8     104 in 1987    107 in 1996    106 in 1996
Oct 9     103 in 1996    106 in 1996    104 in 1996

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ530>544-546-
     548>551-553>555-559.

CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ562-566-567-
     569-570.

&&

$$

DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Benedict/RW
CLIMATE...18