879
FXUS65 KPSR 012315
AFDPSR

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

.UPDATE...
Updated Aviation...

&&

.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 2315Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Low confidence forecast with respect to wind shifts as the influence
from isolated showers across lower elevations combine with outflows
originating over higher terrain. Compared to previous days, gusts
should be less pronounced and boundaries slower moving with a
tendency for stalling. Forecast trends suggest SW winds more
predominant during the late afternoon with variability becoming more
common into the early evening. Models suggest a shift to easterly by
late evening, however timing is quite uncertain. Otherwise, there is
only around 15% chance of SHRA/TSRA directly affecting an aerodrome
this evening. Clouds decks will remain above 8K ft and gradually
thin through Tuesday as storm activity becomes even more removed
from terminal locations.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Tuesday afternoon under
clear skies. Wind directions will favor the typical variation
between SE and SW with occasional afternoon/evening gusts to around
20kt.

&&

.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...18
FIRE WEATHER...Berislavich