246
FXUS65 KPSR 030507
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1005 PM MST Tue Jul 2 2024

.UPDATE...
Updated Aviation

&&

.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 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 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...18
FIRE WEATHER...Kuhlman/Lojero