856
FXUS65 KPSR 040914
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
214 AM MST Thu Jul 4 2024

.SYNOPSIS...
A strong high pressure system will overtake the region over the
next few days resulting in unseasonably dry conditions and even
hotter temperatures. This will lead to excessive heat conditions
building across the majority of the region starting today and
likely lasting through at least the early part of next week as
high temperatures across a good portion of the lower deserts reach
or even exceed 115 degrees.

&&

.DISCUSSION...
An unseasonably strong high pressure ridge meeting climatological
record H5 heights off the California coast of up to 599dm has
overtaken the majority of our region. Very dry air has surged
southward through southern California and all of Arizona except
for the southeastern portion of the state. Aside from some very
shallow boundary layer moisture reemerging since late last
evening, daytime surface dew points will drop into the 40s to
around 50 degrees this afternoon and then plummet to between 25-35
degrees on Friday. This amount of dry air will push PWATs down to
as low as 0.5" in the Phoenix area on Friday, well below the
1.4" or above typically needed for monsoon activity.

Given the very high heights aloft and the drying of the
atmosphere, air temperatures will respond over the next couple of
days with readings easily topping 115 degrees over much of the
lower deserts of southeast California and southwest Arizona to
111-116 degrees across the south-central Arizona lower deserts.
The hottest day is likely to be Friday when we see the lowest
dew points. It would not be surprising to have some areas west of
the Colorado River reach 120 degrees on Friday. This building
heat will cause the areal coverage of Major HeatRisk to expand
considerably through Friday with the majority of the lower
deserts crossing over the threshold considered for excessive heat.

Forecast temperatures through at least next Tuesday do not vary
much more than a couple degrees with highs each day generally
ranging from 113-120 degrees across southeast California and far
southwest Arizona to 111-116 degrees across south-central Arizona.
Lower level moisture is likely to rebound slightly over the
weekend into early next week as we get brief bouts of moisture off
the Gulf of California, but all that will do it make it feel a
little less dry. Clear skies are likely to persist through the
weekend and possibly longer depending on how the proximity of any
storm activity over New Mexico and far southeast Arizona.

The strong high pressure ridge is forecast to very slowly shift
eastward through California reaching western Arizona at some point
early next week, but it will also weaken some during that period.
H5 heights for our region should stay very steady at between
594-596dm through at least early next week, likely longer. As the
ridge center moves into Arizona (likely northern Arizona) by the
middle of next week, this should allow for some additional
moisture to begin seeping into southeast Arizona to as far north
as the Mogollon Rim. This should provide for a modest return of
showers and storms over the higher terrain as early as next
Tuesday, but that timing may be a bit optimistic. A north to
northeasterly steering flow will likely prevent any activity from
reaching the south-central Arizona lower deserts for the first
few days, but gradually (late next week or next weekend) chances
may spread into the Phoenix area. Forecast temperatures during
the latter half of next week do gradually lower, but it still
seems probable that the Excessive Heat Warning will have to get
extended further, especially across the western deserts.

&&

.AVIATION...Updated at 0505Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Thursday night with
daytime cloud decks relegated to mountains well east of the
terminals. West winds should predominate for the majority of the TAF
period with only a brief period of light easterly or variable winds
around sunrise. Occasional gusts up to 20kt will be possible.

Southeast California/Southwest Arizona including KIPL and KBLH:
No significant weather concerns will exist through Thursday night
under clear skies. A SE wind component will be preferred at KIPL
with some variation between SE and SW at KBLH. Occasional
afternoon/early evening gusts around 20kt should be expected.

&&

.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.

     Excessive Heat Warning from 10 AM this morning to 8 PM MST
     Tuesday for AZZ531>555-559.

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

     Excessive Heat Warning from 10 AM this morning to 8 PM PDT
     Tuesday for CAZ560-561-563>565-568.

&&

$$

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