914
FXUS65 KPSR 091155
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
455 AM MST Fri May 9 2025

.UPDATE...Updated 12Z Aviation Discussion.

&&

.SYNOPSIS...
As high pressure strengthens over the region into the weekend, we
can expect hot temperatures with highs around 100 degrees today
and to around 105 degrees over the weekend. This will result in
widespread Moderate to even localized Major HeatRisk across the
lower deserts. Skies will remain clear through Saturday before
some higher level clouds roll in for Sunday. Winds will also
become breezy starting Saturday and continue into early next week
as an incoming dry weather system eventually brings some cooler
air back into the region.

&&

.DISCUSSION...
Upper level ridging has fully spread over the Desert Southwest
with H5 heights rising to between 582-584dm. Further strengthening
of the ridge is anticipated today into the weekend as it is
forecast to peak between 585-587dm, or just into the 90th
percentile of climatology for this time of year. For today, we
should see much of the warmer air aloft from the ridge mix down
resulting in highs at or just above 100 degrees across the lower
deserts raising our HeatRisk into the Moderate category. As
heights aloft increase into the weekend, we will see additional
warming pushing our highs a few degrees higher with the hottest
temperatures of 102-107 degrees across the lower deserts of
southeast California and southwest Arizona and 100-105 degrees in
Phoenix. This should result in some very localized areas of Major
HeatRisk for both Saturday and Sunday, but the bulk of the area
will still fall under a Moderate HeatRisk. Skies are expected to
be clear on Saturday before we see increasing higher level clouds
on Sunday which could keep some areas from reaching the current
NBM forecast highs.

Winds are forecast to become quite breezy out of the east
southeast across much of southern and central Arizona starting
around sunrise Saturday morning. This will mainly be in response
to an increasing gradient between our high pressure ridge and a
strengthening low over the Lower MS River Valley. Wind gusts of
25-35 mph will be possible mainly during the mid morning timeframe
before winds begin to drop off into the afternoon. A similar wind
set up is likely for Sunday morning but speeds look to be around
5 mph less.

Model guidance also shows a deep Pacific trough reaching the
Pacific Northwest early in the weekend before nearing our region
on Sunday. Despite the trough weakening as it moves inland, we
will begin to see decent height falls by Sunday afternoon leading
to increased southwesterly winds across the western deserts. As
the trough begins to shift more into the Great Basin on Monday,
height falls will pick up across our region leading to some modest
cooling and breezy conditions areawide. Ensembles still agree
this next Pacific trough will be fairly slow to fully move through
our region, likely not until next Tuesday or Wednesday. There is
still some uncertainty with the exact timing and the depth of the
system, with NBM temperatures slowing the cool down early next
week, but we are likely to see highs eventually drop into the 80s
by Wednesday.

&&

.AVIATION...Updated at 1155Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
Winds at all terminals will predominately exhibit an easterly
component through the TAF period. Wind speeds will mainly be aob
10 kt, with the exception of some gusts later this morning due to
a backdoor front moving across the area. This backdoor front will
cause ESE gusts of 15-20 kt between 15-18Z this morning. A period
of light and variable winds is expected this evening. Skies will
remain mostly clear with FEW clouds with bases aoa 13-15 kft
moving in this evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
Wind speeds at both terminals will generally be aob 8 kt through
the TAF period. Current westerly winds at KIPL will become light
and variable by the mid-morning hours. Winds may tend to be more
out of the NE from 20-24Z this afternoon, and a TEMPO group has
been introduced to show this. At KBLH, current northwesterly winds
will go northeasterly later this morning (around 16Z) and then go
back northwesterly late this evening (around 05Z). Skies will
remain mostly clear.

&&

.FIRE WEATHER...
High pressure will strengthen over the region into the weekend
leading to hot temperatures and highs topping 100 degrees over
the majority of the lower deserts through Sunday. Humidities will
drop a bit further today with MinRHs around 15% before dropping
closer to 10% by Sunday. After light winds today, winds will
become quite breezy out of the east on Saturday with peak gusts
of 25-35 mph during the morning hours across portions of southern
Arizona. Expect another round of easterly breezy conditions
Sunday morning across eastern Arizona before breezy conditions
expand to include the western districts Sunday afternoon. These
conditions may lead to a period of elevated fire danger in some
areas this weekend. An approaching low pressure system early next
week will lead to a cooling trend, but also more breezy to windy
conditions which will likely bring a continuation of the elevated
fire danger.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Berislavich
FIRE WEATHER...Kuhlman