142
FXUS65 KPSR 042312
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Thu Jul 4 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
A strong high pressure system building over the region will result
in unseasonably dry conditions and very hot temperatures for the
next several days. This will lead to excessive heat conditions
building across the majority of the region, which is expected to
last through the weekend and at least through the first half of next
week as temperatures across the majority of the lower desert
communities approach or even exceed 115 degrees.

&&

.DISCUSSION...
A strong high pressure centered near the central California coast
has overtaken the majority of the southwestern CONUS. This feature
is producing a northerly wind flow, which has pushed most of the
monsoonal moisture southward into northern Mexico. As a result,
mainly clear skies with near zero storm activity is expected
beginning today. Temperatures this afternoon will range between 110-
116 degrees across the lower deserts. Temperatures of these
magnitudes are expected to result in areas of major HeatRisk with
excessive heat warnings in effect across all of the lower desert
communities. Thus, people taking part in the 4th of July festivities
are urged to take all the necessary heat precautions to avoid any
heat-related illness.

Unfortunately, the excessive heat conditions are expected to
continue into the weekend and through at least the first half of
next week. The high pressure ridge into early next week is forecast
to park itself over the Great Basin Region with 500 mb height fields
across the region expected to range between 594-597dm. In addition,
with the northerly flow persisting, a very dry air mass will persist
with PWAT values across the region ranging between 0.5-0.9", which
is well below normal for this time of the year. Thus, mostly clear
skies and near zero storm activity is expected for the majority of
the region. The enhanced 500 mb height fields along with the mostly
clear skies will result in high temperatures to range between 112-
117 degrees across south-central AZ and between 115-120 degrees
across the western deserts. It won`t be surprising that some of the
desert locations in southeast CA approach 120 degrees.

Model guidance heading into the middle to latter half of next week
is hinting that the ridge will gradually migrate eastward, which
will allow for a more favorable flow pattern for moisture to return
and thus storm chances, especially across the higher terrain  areas
of eastern AZ. There is still uncertainty with the timing of
eastward shift of the ridge, which will determine when the moisture
begins to move back in, thus helping to lower the temperatures
somewhat. For the lower desert locations, it may not take until the
end of next week or the following weekend for temperatures to lower
below excessive heat thresholds. This scenario is currently being
shown by the latest NBM deterministic, which shows high temperatures
across the lower deserts continuing at 115+ degrees through the
latter half of the week. Thus, the current Excessive Heat Warnings
that in effect through Tuesday may need to be extended further.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather issues will exist through Friday afternoon as only a few
distant cloud decks form over mountains east of the terminals. West
winds with occasional gusts around 20kt will be common through mid
evening before gradually weakening. Confidence is much better that
an east wind trajectory develops overnight, however the transition
may be much later than usual. Overall wind speeds will be weaker
Friday with limited or no enhanced gusts.


Southeast California/Southwest Arizona including KIPL and KBLH:
No significant weather concerns will exist through Friday afternoon
under clear skies. A SE wind component will be preferred at KIPL
with some variation between SE and SW at KBLH. Extended periods of
variable directions may be common across the region.

&&

.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 112-117
degrees are expected across the lower deserts each day through early
next week. Daily MinRH values through the weekend will fall between
5-15% across the lower deserts, while higher terrain areas in
Arizona will mostly see 10-20%. Winds will 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 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>555-559.

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

&&

$$

DISCUSSION...Lojero
AVIATION...18
FIRE WEATHER...Kuhlman
CLIMATE...Kuhlman