965
FXUS65 KPSR 040505
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 PM MST Wed Jul 3 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Strong high pressure system building across the region through the
end of the week will result in drying conditions and hotter
temperatures. This will result in excessive heat conditions building
across the majority of the region starting on Thursday and likely
lasting through at least the first half of next week as high
temperatures across the majority of the lower desert locations
approach 115+ degrees.

&&

.DISCUSSION...
A strong high pressure system, currently sitting just off the
California coast, will gradually increase the northerly flow across
throughout the day, with drier air being advected into the region.
Latest SPC mesoanalysis shows PWATs across south-central AZ ranging
between 1.0-1.2" and it is expected that these values continue to
drop during the next couple of days. In terms of storm chances this
afternoon, with the drier surge of air, activity will be very
isolated with a slight chance of a thunderstorm developing across
southern Gila County. Otherwise, a fairly tranquil weather day is
expected throughout the region.

The main concern heading through the next several days will continue
to be the excessive heat that is expected to materialize across the
majority of the region. As high pressure just off the west coast
of California continues to gradually shift eastward into the Great
Basin Region through the end of the week and the upcoming weekend,
northerly flow will continue to maintain a fairly dry air mass in
place with mostly clear skies and near zero storm activity. The
mostly clear skies along with 500 mb height fields across the region
increasing to 594-597dm will cause surface temperatures to increase.
Highs across most of the lower desert communities will likely
approach 115 degrees with the potential that some of the deserts of
southeast CA approach 120 degrees. Temperatures this high will
increase the HeatRisk into the major category with some localized
areas reaching the extreme category. This signifies that most of the
general population will be at risk of heat-related impacts if the
proper precautions are not taken. As a result of the extreme heat
expected to materialize, Excessive Heat Warnings are in effect
through at least next Tuesday.

Heading into next week, ensemble guidance continues to be in
excellent agreement in showing the ridge of high pressure remaining
parked over the Great Basin at least through the first half of the
week with not much change in the overall temperatures. Thereafter,
there are signs that by the middle to latter half of next week the
ridge axis will gradually migrate eastward to the point that a more
favorable moisture return pattern will more likely set up across the
region. Timing out when this will occur is still a bit uncertain at
this time. However, once the moisture increases and storm activity
in concert picks up, we should see some cooling in the overall high
temperatures. If the overall moisture return is delayed until the
end of the week, then there is the potential that the Excessive Heat
Warnings that are currently in effect through next Tuesday could be
extended another day or two next week.

&&

.AVIATION...Updated at 0505Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Thursday night with
daytime cloud decks relegated to mountains well east of the
terminals. West winds should predominate for the majority of the TAF
period with only a brief period of light easterly or variable winds
around sunrise. Occasional gusts up to 20kt will be possible.


Southeast California/Southwest Arizona including KIPL and KBLH:
No significant weather concerns will exist through Thursday night
under clear skies. A SE wind component will be preferred at KIPL
with some variation between SE and SW at KBLH. Occasional
afternoon/early evening gusts around 20kt should be expected.

&&

.FIRE WEATHER...
Drier conditions will continue to filter into the region through
Thursday leaving only slight chances for some showers and maybe a
weak thunderstorm across the eastern Arizona high terrain this
afternoon. Rain chances will generally come to an end altogether
starting Thursday. As conditions continue to dry out, hotter
temperatures are expected with excessive heat spreading eastward
through much of Arizona. MinRH values across the lower deserts will
fall to around 15% today, while higher terrain areas east of Phoenix
see 20-25%. Winds will follow diurnal trends, occasionally gusting
to 20 mph during the afternoon hours. MinRHs starting Thursday will
mostly be between 10-15% over the lower deserts to 15-20% over
higher terrain areas. Temperatures by Thursday and through early
next week are expected to be well above normal with lower desert
highs over the eastern districts up to around 115 degrees and even
hotter over some of the western districts. The combination of the
very hot and dry conditions through the next several days will to an
increased fire danger threat.

&&

.CLIMATE...

Record Highs

           Phoenix      Yuma      El Centro
          ---------    -------   ------------
July 4    118 (1989)  117 (1957)  117 (1969)
July 5    116 (1983)  116 (1905)  115 (2007)
July 6    116 (1942)  117 (2018)  118 (1966)
July 7    118 (2017)  118 (2017)  121 (2017)
July 8    115 (1985)  118 (1958)  117 (1942)
July 9    116 (1958)  119 (1958)  117 (1958)
July 10   115 (1958)  118 (1959)  116 (2021)

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ530.

     Excessive Heat Warning from 10 AM Thursday to 8 PM MST Tuesday
     for AZZ531>555-559.

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

     Excessive Heat Warning from 10 AM Thursday to 8 PM PDT Tuesday
     for CAZ560-561-563>565-568.

&&

$$

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