558
FXUS65 KPSR 110958
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
258 AM MST Thu Jul 11 2024

.SYNOPSIS...
Strong high pressure will continue to impact the region over the
next few days allowing excessive heat to persist across the region
through at least Friday. Modest moisture levels will also provide
for chances for isolated thunderstorms over eastern Arizona high
today and gusty winds as far west as the Phoenix area. For Friday
and through the weekend, moisture levels will continue to improve
as rainfall chances eventually spread over the rest of the
region. Temperatures will also gradually cool away from excessive
levels and closer to seasonal normals by Sunday.

&&

.DISCUSSION...
The strong high pressure system currently centered near Las Vegas
continues to be the dominant feature across the region, but day by
day moisture levels are improving and this will eventually curtail
the excessive heat that has been a problem over the last week or
so. Convective activity yesterday was fairly limited in scope and
impacted areas well north and southeast of Phoenix. Increased
moisture levels today are expected to bring a bit more widespread
convection, initially focused along the Mogollon Rim to the White
Mtns. Forecast MUCAPE of around 1000 J/kg across the majority of
southern Arizona along with 20-30kt mid-level winds out of the
north northeast in eastern Arizona should promote isolated strong
to possible severe thunderstorms over the high terrain by mid to
late afternoon. The dry lower levels will again support very high
DCAPEs increasing the strong wind threat. The 00Z HREF generally
shows two main areas of convection, one north northeast of Phoenix
and another over southern Gila County into eastern Pinal and
Graham Counties. Given the expected high CIN in place over the
south-central Arizona lower deserts, any storms coming off the
high terrain are expected to die out quickly, but strong outflow
winds moving into the lower deserts are very likely. Guidance
generally supports the strongest outflow winds across central
Pinal County with another likely weaker outflow potentially
moving southwestward into northern Maricopa County.

Moisture levels will continue to improve into Friday, especially
across the lower deserts as guidance shows a robust Gulf moisture
surge occurring tonight/Friday morning. Convective potential over
the higher terrain for Friday seems to be very similar to today
minus less activity in far southeast Arizona due to a pocket of
drier air moving out of west Texas and northern Mexico. The chance
for strong to severe storms on Friday looks to be considerably
lower due to lower instability and DCAPEs, but better moisture and
lower CIN over the lower deserts may be enough for some storms to
survive or to develop along propagating outflows into the south-
central Arizona lower deserts.

Excessively hot temperatures will persist through at least Friday
with highs gradually lowering each day as lower level moisture
increases. Forecast highs today are again between 112-116 degrees
in the Phoenix area to 114-119 degrees across the western deserts
before some improvement is seen on Friday across the western
deserts. Surface dew points increase a good amount into Saturday
with readings in the 60s across the western deserts to the mid to
upper 50s in the Phoenix area. Forecast highs Saturday do take a
decent step lower with readings mostly between 110-113 degrees,
but given the increased humidities it really won`t feel any cooler
than Friday. The one upside starting Saturday is there should be
some cloud cover at times and this could help to take the edge off
the heat.

Forecast confidence for convection over the weekend has decreased
as model guidance is now shifting the expected development of an
upper level low from over New Mexico to over Texas. Guidance is
now also hinting at a quiet day across at least southeast Arizona
on Saturday due to the pocket of drier air, despite our flow
turning solidly out of the east. An easterly flow is almost
always favorable for monsoon activity, but given the models
shifting toward a brief period of drying into eastern Arizona
Saturday`s convection is probably going to be fairly limited.
Moisture advection should improve once again Saturday night into
Sunday across the entire area creating better storm chances later
Sunday, but likely losing support of the upper low (now probably
too far east) may hinder widespread development. However, with
deeper moisture likely in place by Sunday afternoon, as long as
the higher terrain convection is widespread enough, any colliding
outflows over the lower deserts should result in additional
development. Locally heavy rainfall may also become a concern on
Sunday along with a strong wind threat from any stronger storms
that may develop. Drier air is expected to gradually spread from
west to east early next week likely limiting convection to south-
central and eastern Arizona by Tuesday. Temperatures are also
expected to continue to improve Sunday into Monday with highs
falling below 110 degrees over the south-central Arizona lower
deserts to around 110 degrees over the western deserts. If
guidance is correct in showing the drier air by next Tuesday or
Wednesday, then that should eventually push temperatures up a few
degrees during the middle of next week.

&&

.AVIATION...Updated at 0547Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation weather concern through the period will be
the potential for gusty outflows tomorrow during the late
afternoon into the evening. Winds through tomorrow afternoon will
favor diurnal tendencies with some light and variable winds at
times. Uncertainty increases going into the late afternoon and
into the evening Thursday with the potential for several outflows
to push into the Valley. An east to southeast outflow currently
looks to be the most favored direction, though confidence in exact
timing and magnitude is low. There is about a 30-40% chance of
seeing outflow gusts in excess of 30 kts. Otherwise, mostly clear
skies will continue with FEW-SCT mid and high clouds at times.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected through the next 24
hours. Winds at KIPL will continue to favor an E to SE component,
while winds maintain a S component at KBLH. Winds will remain
elevated at KBLH with sustained speeds up to around 10-12 kts.
Otherwise, mostly clear skies will persist with a FEW mid and high
clouds at times.

&&

.FIRE WEATHER...
Unusually hot weather will persist the next few days with
thunderstorm activity steadily increasing over eastern districts.
Moisture will steadily increase over most districts through the
weekend allowing temperatures to retreat while humidity levels and
rainfall chances increase markedly. Storms will initially produce
only isolated wetting rain chances in eastern districts with areal
coverage likely becoming far more widespread by the weekend. Minimum
humidity values will continue to fall into a 5-15% range through
Friday, however by Sunday, values should struggle to fall below 20%.
Some slight drying may wash over the districts by the middle of next
week when minimum values fall closer to a 10-20% range. Occasional
afternoon upslope gusts near 20 mph will be common the next few
days, and the increase in thunderstorm activity will produce more
frequent strong outflow winds across a larger expanse.

&&

.CLIMATE...

Record Highs

           Phoenix      Yuma      El Centro
          ---------    -------   -----------
July 11   118 (1958)  118 (1958)  117 (1975)
July 12   116 (2020)  119 (1939)  118 (1964)

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530>555-559.

CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ560>570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...18/Kuhlman
CLIMATE...Berislavich/Kuhlman