274
FXUS65 KPSR 022047
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
147 PM MST Tue Jul 2 2024

.SYNOPSIS...
Enough moisture will still be present through Wednesday
to generate some afternoon convection over the higher terrain areas.
Starting on Thursday and continuing into the weekend and through
most of next week, as strong high pressure builds over the region,
much drier air will result near zero storm chances. Along with the
drier air will come hotter temperatures as highs across the lower
deserts are expected to top out at 115+ degrees, resulting in
excessive heat conditions.

&&

.DISCUSSION...
Latest water vapor satellite imagery as well as streamline analysis
currently show a trough situated over the northern Plains with a
strong ridge of high pressure off the California coast. Our region
is currently under southwesterly flow aloft as a result of the
trough to the north and thus drier air is gradually making its way
eastward into Arizona. This is reflected well in the latest SPC
mesoanalysis which shows PWATs across south-central AZ ranging
between 1.1-1.5", which is a significant drop from the near 2"
that was present yesterday. Despite this drop in moisture, enough
will still be present to allow for the development of afternoon
convection across the higher terrain areas east of Phoenix. Gusty
winds and localized heavy rainfall will continue to be the main
threat with the storms. Although the south-central AZ lower
deserts are expected to be spared from storm activity, outflows
emanating from the higher terrain activity may still make its way
into the lower deserts with the latest HREF indicating about a 30%
chance of winds of 35+ mph. Heading into Wednesday, as the
aforementioned ridge of high pressure off the Pacific moves closer
to the California coast, the overall flow will switch out of the
north, which will push in drier air with PWATs across south-
central AZ dropping to around 1". This will decrease storm chances
even further across the higher terrain areas with NBM PoPs below
20%.

Starting on Thursday and continuing through the upcoming weekend, as
the ridge settles over California/Nevada, northerly flow will scour
out any lingering boundary layer moisture, which will essentially
end storm chances. The main concern then switches over to the
excessive heat. 500 mb height fields are expected to build into
the 594-597dm range. This will result in hotter temperatures with
a lot of the lower desert communities forecast to see
temperatures rise to near 115 degrees, with the potential for some
of the western deserts to approach 120 degrees. This will result
in a more widespread areal coverage of major HeatRisk. Excessive
Heat Warnings are in effect for all of southeast CA with an
Excessive Heat Watch in effect for southwest and south-central AZ
(expected to be upgraded to a warning within the next 12-24
hours). Therefore, given the excessive heat conditions expected to
materialize, it is very essential for anyone planning outdoor
activities during the Holiday Weekend to take all the necessary
heat precautions to avoid any heat-related illnesses.

Heading into next week, ensembles are in excellent agreement in
showing the ridge parked over the Great Basin Region, with a dry
northerly flow persisting through the majority of next week. Thus,
storm chances will continue to remain null with excessive heat
conditions continuing as highs across the majority of the lower
desert communities remain or even exceed 115 degrees. The
excessive heat headlines remain in effect through next Tuesday,
however, there is potential that it may need to be extended even
further in time in the following days.

&&

.AVIATION...Updated at 1730Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will continue to follow familiar diurnal tendencies through
the TAF period. Uncertainty exists regarding our usual E`rly
shift, with morning hi-res guidance showing a weak outflow from
distant thunderstorms turning winds earlier than normal between
03-04Z, while more recent guidance shows a more typical outcome,
with the E shift occurring closer to 07-09Z. TAFs currently
reflect the later switch, but amendments may be needed if any
outflows occur. Gusts with potential outflows may reach into the
upper teens to around 20 kts but outside of that, wind speeds
should generally be aob 10 kts. FEW mid and high level clouds will
be present through Wednesday morning, with the lowest bases
around 12 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at IPL will generally be out of the SE through the period,
with perhaps a brief switch to the SW early tonight. At BLH, winds
will follow diurnal trends, with occasional afternoon gusts
upwards of 20 kts. Speeds at BLH may pickup by mid morning
Wednesday, with potential gusts 20-25 kts. Clear skies will
prevail through the current forecast window.

&&

.FIRE WEATHER...
Drier conditions will continue to filter into the region over the
next few days. Isolated afternoon showers and a few thunderstorms
are expected this afternoon over the Arizona higher terrain with
chances on Wednesday even lower. As conditions continue to dry
out, even hotter temperatures are expected, especially later this
week. Humidities will drop considerably today over the majority of
the area. The lower deserts will see MinRHs mostly fall to around
15%, while higher terrain areas east of Phoenix will see 25-35%.
Winds will follow diurnal trends, occasionally gusting to 20 mph
during the afternoon hours. Starting Thursday, essentially all of
the monsoon moisture will get ejected from the area leaving very
dry and hot conditions, likely well into next week. MinRHs
starting Thursday will mostly be between 10-15% over the lower
deserts to 15-20% over higher terrain areas. The dry air will also
end any rain chances during this time. Temperatures are expected
to climb to well above normal by Thursday with lower desert highs
between 112-120 degrees.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ530.

     Excessive Heat Watch from Thursday morning through Tuesday
     evening for AZZ531>544-546-548>551-553>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...Lojero
AVIATION...RW
FIRE WEATHER...Kuhlman/Lojero