096
FXUS65 KPSR 032029
AFDPSR

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

.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 1752Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through the TAF
period. Winds are now switching to a westerly component this
morning and will continue to predominantly favor the west through
the rest of the TAF period. Expect to see a few occasional gusts
this afternoon to around 20 kts, which may linger into the evening
before subsiding. Confidence is low that there will be a diurnal
easterly switch overnight tonight with perhaps a period of light
and variable winds before resuming out of the west once again by mid
morning tomorrow. Otherwise, mostly clear skies with a few
passing mid clouds are expected through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours. Winds at KIPL will persist out of the E/SE while winds
at KBLH favor the S through the period. Wind speeds will increase
up to 10-15 kts this afternoon and evening, with gusts up to
around 20-25 kts at KBLH. SKC conditions will persist.

&&

.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...Smith
FIRE WEATHER...Kuhlman/Lojero
CLIMATE...Kuhlman