717
FXUS65 KPSR 031005
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
305 AM MST Wed Jul 3 2024

.SYNOPSIS...
Drying conditions will continue over the next couple of days with
limited shower activity mainly over higher terrain areas. Strong
high pressure will also build into the region through the end of
the week leading to even hotter temperatures and expanding
excessive heat over all of the lower deserts starting Thursday.
Excessive heat conditions are expected to prevail through the
weekend into next week with highs across the lower deserts likely
topping 115 degrees in some locations.

&&

.DISCUSSION...
The excessive heat conditions remain the main forecast concern
through at least early next week as a current record strong high
center off the California coast gradually shifts eastward into our
region over the next several days. Dry air has worked its way
into much of the region over the past day and half, but modest
monsoon moisture still remains in place across southeast Arizona.
In fact, we are currently seeing some shallow moisture advection
working its way into the Phoenix area with more moisture seeping
off the GoC into southwest Arizona later this morning. This
increase in shallow moisture will be short-lived however as
northerly flow increases west to east today bringing in another
surge of dry air. Through this afternoon some mostly isolated
light showers will continue to be possible south and east of
Phoenix where there is enough lingering moisture present.

Temperatures will continue to inch upward over the next several
days as the high pressure ridge overtakes the region. The slight
boost in moisture today should keep temperatures similar to
yesterday`s highs, but it still means most lower desert areas will
top 110 degrees this afternoon to as high as 115 degrees across
southeast California. Scouring out whats left of the boundary
layer moisture Thursday into Friday will make it easier for
temperatures to climb, while also having heights rise due to the
increasing influence of the ridge currently off the West Coast.
High temperatures are expected to climb a degree or two per day
through Friday with readings on the 4th of July ranging from
111-115 degrees in the Phoenix area to 113-118 degrees over the
western deserts. Due to this expected rise in temperatures
starting Thursday, Excessive Heat Warnings will go in effect for
the majority of the area.

From Friday through at least next Tuesday, the ridge center is
forecast to gradually shift eastward reaching southern California
and western Arizona by early next week. Luckily, guidance shows
the ridge weakening some as it comes onshore with the core of the
high dropping to around 596dm. However, during this entire period
our region will see H5 heights ranging from 593dm across eastern
Arizona to 596dm in southeast California. For some prospective,
these heights are fairly common for our region during the summer
and barely even make it into the 90th percentile of climatology.
However, because we lose our moisture temperatures will more
easily climb upward with these increasing heights, likely flirting
with daily record highs starting Friday and lasting through a good
portion of next week. NBM forecast highs starting Friday rise to
112-116 degrees across the south-central Arizona lower deserts to
115-120 degrees across far southwest Arizona and southeast
California. At the moment, there is very little variation in
forecast highs from Friday through the middle of next week, so
it`s quite likely the current Excessive Heat Warning which goes
through next Tuesday will end up getting extended. This heat will
increase the HeatRisk into the Major category for much of the
area from Phoenix westward by Friday with even portions of
southeast California bumping up into the Extreme category. Model
guidance does start to indicate some potential monsoon moisture
returning into southern Arizona at some point late next week or
the following weekend, but that will all depend on how long it
takes for the ridge center to shift far enough east of the area.

&&

.AVIATION...Updated at 0505Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No significant weather issues will exist through Wednesday night
with cloud decks concentrated mainly over higher terrain areas east
of the terminals. A long traveling outflow will induce an easterly
component across the metro around midnight with good confidence that
directions will revert back to a westerly direction much earlier
than usual mid/late Wednesday morning. Occasional gusts 15-20kt will
be common again during the afternoon/early evening. Storms and
outflow winds should not be an issue for the metro aerodromes
Wednesday.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Wednesday night under
clear skies. Confidence is good that winds should revert to a S/SE
direction overnight with variability likely becoming more common
towards sunrise. Only modest occasional afternoon/evening gusts
should be experienced Wednesday with typical veering to a SW
direction during the evening.

&&

.FIRE WEATHER...
Drier conditions will continue to filter into the region through
Thursday leaving only slight chances for some showers and maybe a
weak thunderstorm across the eastern Arizona high terrain this
afternoon. Rain chances will generally come to an end altogether
starting Thursday. As conditions continue to dry out, hotter
temperatures are expected with excessive heat spreading eastward
through much of Arizona. MinRH values across the lower deserts
will fall to around 15% today, while higher terrain areas east of
Phoenix see 20-25%. Winds will follow diurnal trends,
occasionally gusting to 20 mph during the afternoon hours. MinRHs
starting Thursday will mostly be between 10-15% over the lower
deserts to 15-20% over higher terrain areas. Temperatures by
Thursday and through early next week are expected to be well
above normal with lower desert highs over the eastern districts
up to around 115 degrees and even hotter over some of the western
districts.

&&

.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 Thursday 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 Thursday to 8 PM PDT Tuesday
     for CAZ560-561-563>565-568.

&&

$$

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