103
FXUS65 KPSR 012046
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
146 PM MST Mon Jul 1 2024

.SYNOPSIS...
Isolated shower and thunderstorm activity is expected this
afternoon and evening across south-central Arizona. Daily rainfall
chances will last into Wednesday, with most activity becoming
focused over higher terrain locations. High pressure will usher in
a period of drying later this week, with rain chances becoming
more muted areawide by the 4th of July. Above-normal temperatures
will persist over the next several days, with excessive heat
conditions for parts of southeast California and the Lower
Colorado River Valley.

&&

.DISCUSSION...
Current atmospheric analysis reveals the persistent sub-tropical
ridge continuing to center itself over the Southern Plains, while a
weak area of troughing migrates across the Intermountain West. This
disturbance will break the pattern that we have seen over the past
several days, helping to erode positive height anomalies over the
Desert Southwest, and pushing the stubborn high pressure toward
the southeastern CONUS. Drier air will also accompany this
troughing, slowly spreading across our forecast area over the
next few days. There is already a noticeable moisture gradient
being observed across the region, with PWATs of 0.7-0.8" over
southeastern California, reaching towards 1.9-2.0" over south-
central Arizona. Before these drier conditions become fully
encompassed across Arizona, afternoon shower thunderstorm activity
will once again be possible today within the axis of greatest
moisture.

Hi-res guidance shows a plume of instability setting up over much of
south-central, and parts of southwest Arizona, with MUCAPE values
ranging between 750-1000 J/kg. Model soundings and HREF guidance do
indicate a little CIN this afternoon, but the environment should be
mostly uncapped, priming the atmosphere for at least some
convective development. There will not be much large-scale ascent
to promote widespread convection, so the most likely initiating
mechanism will be enhanced terrain features, with coverage
remaining generally isolated. The consensus among ensemble members
is that showers and thunderstorms will develop across the the
high terrain areas east of Phoenix, and around terrain features in
southwest Maricopa and Pinal Counties. With steering flow
becoming more southwesterly, a few storms that develop southwest
of Phoenix may move over the metro, but not everyone will see
rainfall. The main concerns with this round of activity will be
heavy downpours, gusty winds, and localized areas of blowing dust.
The morning Phoenix soundings showed DCAPE values around 800
J/kg, favorable for some marginally strong downbursts. However,
model soundings for this afternoon have values rising towards 1300
J/kg, which would be supportive of stronger thunderstorm
outflows. As a result, the HREF is highlighting most of Maricopa,
Pinal, and Gila Counties in a 30-60% chance of seeing outflow
gusts exceeding 35 mph. It would also not be surprising to see
isolated instances of minor flooding due to ample moisture
availability, and weak steering flow, resulting in some heavy,
slow-moving showers and storms

Rain chances will continue to decrease over the next few days as dry
air continues to push across the region. Any further rainfall
activity through Wednesday will be focused primarily over the
Arizona high-terrain. Further drying is expected to occur later in
the week as a strong area of high pressure stretches from the
Eastern Pacific toward the Great Basin, shifting flow across the
Desert Southwest out of the north. PWATs by the 4th of July will
approach seasonal normals, with most remaining moisture confined
in the boundary layer, muting rain chances even further as
regionwide PoPs for Thursday and Friday drop to 10% or less.

Temperatures through the week will follow a gradual warming trend,
with today likely being the "coolest" over the next several days.
Lower desert highs this afternoon will range between 103-107
degrees across south-central Arizona, while highs closer to 110
degrees can be expected further west, before these higher readings
become more common across the remainder of the lower elevations
through the middle of the week. Temperatures will climb even
further once the previously-mentioned area of high-pressure
extends closer to our forecast area, with Friday likely being the
hottest day so far this year for many areas, especially out in
southeast California. Temperatures near and in excess of 115
degrees will be common, with some communities potentially reaching
120 degrees. These abnormally hot conditions will result in
widespread coverage of Major HeatRisk, especially over the western
Deserts. An Excessive Heat Warning remains in effect for parts of
southeast California through Friday. It is likely that this
warning will need to be extended both in time and area to
accommodate for the dangerous heat.

&&

.AVIATION...Updated at 1745Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Wind pattern through the forecast period will exhibit diurnal
tendencies with speeds aob 10 kts. There is a slight chance (15%)
of TSRA activity, mainly from 22-02z, but confidence in occurrence
is too low at this time to include in TAF package. There is a
better chance for TSRA activity east of Phoenix, which could send
an outflow boundary into the metro this evening but confidence of
occurrence is low as well. If an outflow boundary were to impact
the metro, wind direction would most likely shift out of east
this evening. Otherwise, conditions should remain relatively
tranquil with lowest cloud bases remaining aoa 10 kft, with SCT to
occasionally BKN coverage prevailing through this evening before
diminishing to FEW during the overnight period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation weather concerns under mostly clear skies expected
through the TAF period. Winds will favor the typical diurnal
tendencies with occasional afternoon gusts upwards of 20-25 kts
at KBLH.

&&

.FIRE WEATHER...
Moisture levels remain high today with additional chances for
isolated to scattered showers and storms and gusty outflow winds
late this afternoon and evening across south-central Arizona. Min
RHs will be in the 25-25% range over south-central Arizona and in
the teens across southeastern California and far southwestern
Arizona.Overnight recovery will be good and in the 40-60% range in
the eastern districts and in the 30-40% range in the western
districts. Outside of thunderstorms, winds will tend to follow
their typical diurnal patterns. Daily monsoon storm chances
continue through Wednesday, although most of the activity will be
confined to the higher terrain locations. Min RHs will be in the
15-25% range Tuesday and Wednesday with overnight recoveries in
the 30-50% range. Dry conditions and ending rain chances start on
Thursday and continue into the weekend. Temperatures will remain
above normal through the week, with Friday being the hottest day
this week.

&&

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

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

&&

$$

DISCUSSION...Berislavich
AVIATION...Lojero
FIRE WEATHER...Berislavich