801
FXUS65 KPSR 051128
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
428 AM MST Fri Jul 5 2024

.UPDATE...Updated 12Z Aviation Discussion.

&&

.SYNOPSIS...
Prolonged extreme heat and dry conditions will continue through
at least early next week with strong high pressure over the
region. Most lower desert locations will see daily high
temperatures between 112 to 120 degrees with limited overnight
relief. A moisture return will bring increased thunderstorm
activity back to the Arizona high terrain and southeast Arizona by
the middle of next week.

&&

.DISCUSSION...
Strong high pressure is currently centered off the NorCal coast
with 594-595dm H5 heights over the Desert Southwest. With a
fairly stagnant hemispheric pattern the strong high pressure is
expected to persist for the next week or longer. Global ensembles
show H5 heights remaining around 594-596dm through this weekend
and all of next week, with a slow drift of the high center east-
southeastward to over the Desert Southwest towards the middle of
next week. Under this setup, prolonged extreme heat conditions are
expected to continue. Excessive Heat Warnings took effect for
most lower desert locations of AZ and Southern CA yesterday and
the warning currently extends through Tuesday next week as
HeatRisk levels push widespread Major to locally Extreme. With
little fluctuation in the synoptic setup, there will be very
little day to day change in temperatures as lower desert highs
push 112-120F and lows fall to lower 80s to lower 90s. Multiple
daily record high and warm low temperatures may be tied or broken
during this stretch of extreme heat (see CLIMATE section below).

During this stretch please protect yourself from the heat.
Hydrate - Hydrate - Hydrate! Avoid strenuous outdoor activities
during the afternoon. Do not leave kids, elderly, and pets in hot
cars. If you do not have personal access to AC, seek out cooling
centers. If you need assistance with heat relief in Maricopa
County, call 211.

In addition to bringing the heat, the high pressure placement has
resulted in dry north to northeast mid-level flow. PWAT values
are on the decline. PWAT with the 00Z Tucson sounding has dipped
below 1.0" and latest objective analysis shows values are down to
0.8-0.9" in South-Central AZ to Southeast CA. PWATs are forecast
to fall even further, down to around 0.6-0.7" this weekend. Normal
PWAT values this time of year is 1.0". This lower moisture, along
with subsidence, will hinder monsoon thunderstorm activity
through early next week.

So, when will this hot and dry pattern change? It is difficult to
say exactly when the heat will abate, as it will likely be
correlated with a return of moisture, clouds, and rain chances.
With the center of the strong high pressure sliding eastward to
over the Desert Southwest toward the middle of next week, there is
potential for excessive heat conditions to continue through the
end of next week. On the moisture side of things, global models
indicate a shortwave trough will round the top of the strong high
and dive through the Southern Rockies into the Southern Plains
Monday, around the same time TC Beryl makes landfall in TX. So, an
increase in storm activity in NM and West TX and steering flow
becoming more northeasterly in NM should help with moisture
fluxes back into AZ from the east. Global models do support rising
PWAT values again beginning the middle of next week, and reaching
back above 1.0" toward the latter half of next week. Still, it
may take a few to several days before monsoon thunderstorm
activity becomes more favorable again in the South-Central AZ
deserts. Activity should increase in Southeast AZ and parts of the
Rim country by the middle of next week and NBM reintroduces
slight chances (20%) for the South-Central AZ lower deserts by the
end of next week.

&&

.AVIATION...Updated at 1125Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Current easterly winds will continue into the afternoon. There
may be a brief period of light and variable winds before
developing a westerly component around 20-21Z. Winds are not
expected to be as gusty as they were yesterday, but there may be
some occasional gusts into the mid teens this afternoon. Winds
will then go back easterly during the overnight hours. Skies will
remain mostly clear through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds speeds will be aob 10 kt through the TAF period. The wind
direction will predominately be out of the southeast into this
evening, with some periods of light and variable winds. This
evening winds will go southwesterly for a few hours before going
back southeasterly at KIPL and southerly at KBLH for the overnight
hours. Skies will remain clear through the period.

&&

.FIRE WEATHER...
Hot and dry conditions will prevail across the area through at least
the weekend as strong high pressure settles in from the northwest.
Excessively hot temperatures with highs generally between 112-120
degrees are expected across the lower deserts each day through at
least early next week. Daily MinRH values through early next week
will fall between 5-15% across the lower deserts, while higher
terrain areas in Arizona will mostly see 10-20%. Winds will be
fairly light and follow diurnal trends, occasionally gusting to
20 mph during the afternoon hours. The combination of the very hot
and dry conditions will lead to an increased fire danger threat.

&&

.CLIMATE...

Record Highs

           Phoenix      Yuma      El Centro
          ---------    -------   -----------
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>555-559.

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

&&

$$

DISCUSSION...Benedict
AVIATION...Berislavich
FIRE WEATHER...Benedict/Kuhlman CLIMATE...Kuhlman