584
FXUS65 KPSR 281158
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
458 AM MST Fri Jun 28 2024

.UPDATE...Updated 12Z Aviation Discussion.

&&

.SYNOPSIS...
Above normal temperatures are likely to persist well into next
week, with many lower desert communities experiencing high
temperatures that approach or exceed 110 degrees each afternoon.
Temperatures Sunday are shaping up to be the hottest over the next
week resulting in an Excessive Heat Watch for portions of
Southeastern California on Sunday and Monday. Unfavorable monsoon
conditions are expected through Saturday with only very minimal
chances for an isolated shower or thunderstorm east and southeast
of Phoenix. Moisture and subsequent rain chances will increase
starting Sunday, likely lasting through the middle of next week.

&&

.DISCUSSION...
The current synoptic pattern continues to show the elongated sub-
tropical ridge stretching across Sonora Mexico northeastward
into Texas. An active wave pattern is also seen across the
Pacific Northwest into the Northern Plains. Between the two
systems, westerly flow will persist across the Desert Southwest
today before beginning to shift more out of the south on Saturday
as the center of the ridge fully establishes itself over Texas and
Oklahoma. The ridge will also quickly strengthen over the
weekend, giving a slight boost to our upper level heights and
temperatures over our region. Forecast highs this weekend look to
rise around a degree a day with Sunday still expected to have the
hottest temperatures with highs of 110-114 degrees across the
lower deserts.

The westerly flow currently over our area continues to bring in
drying aloft, but boundary layer moisture has mostly stuck around.
We have seen surface dew points drop on the order 10 degrees, but
it has not been as much as models had originally forecast. Aside
from the mid level drying, the other main deterrent for monsoon
activity over the past couple of days has been the strong
subsidence aloft provided by the ridge. As the ridge begins to
shift eastward today, subsidence will be less of a factor. Now
with less than expected CIN today and a little better than
previously forecast instability, it seems there may be a slight
chance of some showers and maybe a weak thunderstorm across Pinal
into northeast Maricopa and southern Gila Counties. NBM PoPs of
around 5% do not really represent this potential, but the last
several runs of the HRRR are picking up on some weak afternoon
convection, especially in Pinal County. Have made some upward
adjustments to PoPs to account for this rain potential.

Starting Saturday as the ridge becomes established over the
Southern Plains, an easterly wave is forecast to progress across
northern Mexico likely allowing for considerable convection. Flow
in the mid levels will also turn out of the south southeast into
Arizona on Saturday. Strong moisture advection is then expected to
stream into southern Arizona Saturday night with the help of a
likely MCS south of the border. Between the easterly wave likely
reaching far southeast Arizona on Sunday and PWATs increasing to
around 1.5-1.75", this should provide a good recipe for an active
monsoon day Sunday afternoon into Sunday night across much of
southeast and south-central Arizona. NBM PoPs of 20-40% are likely
underdone for Sunday, but we should have a better idea by this
time tomorrow night. If Sunday ends up being active, then Monday
should be fairly quiet and there are already signs of this
happening within the guidance.

The synoptic pattern will remain favorable for monsoon activity
into the middle of next week as an unseasonably strong ridge
builds off the West Coast and the ridge over the Southern Plains
remains in place. There should also be some northern stream wave
influence into our area around next Tuesday and Wednesday which
would provide for some upper level support for any monsoon
thunderstorm activity. Either or both of those days could end up
being fairly active across south-central and eastern Arizona.
Guidance eventually signals the strong ridge coming ashore into
California late next week providing persistent dry northerly flow
working through Arizona. This should mostly end rain chances over
much of the area by next Thursday for Friday, while temperatures
potentially climb toward the 115 degree mark.

&&

.AVIATION...Updated at 1155Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Current light and variable winds will develop a westerly
component later this morning around 16-18Z. Afternoon breeziness
is once again expected this afternoon, however gusts are only
expected to be around 20 kt today. FEW-SCT mid and high level
clouds will continue to move through the region throughout the TAF
period, and may become BKN at times.

This evening, we will have to watch for the potential development
of isolated to scattered showers and storms to the south and east
of the Phoenix Metro (<15% chance currently). While chances are
low, KIWA would have the best chance to have any impact from these
storms. We will also have to watch for any potential outflow
boundaries, that the storms produce, to move through the Metro

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will follow their typical diurnal patterns through the TAF
period. Speeds will generally be aob 12 kt with the exception of
some gusty winds this afternoon at KBLH with gusts of 20-25 kt.
Skies will remain mostly clear through the TAF period.

&&

.FIRE WEATHER...
Unfavorable monsoon conditions today into Saturday will continue
to lead to clear to mostly clear skies with only minimal (10%)
chances for isolated showers and maybe a thunderstorm across Pinal
and Gila Counties. Above normal temperatures will persist with
readings running 3-5 degrees above normal. Humidities will
continue to drop across the western districts today and likely
into south-central Arizona on Saturday with lower desert MinRHs
between 15-20%. Humidities over the Arizona higher terrain should
stay above 25%. Afternoon breeziness will be common today with
gusts reaching to or just over 20 mph in many locations before
winds settle down a bit on Saturday. Starting Saturday night,
moisture will increase across much of southern Arizona leading to
a return of shower and thunderstorm chances on Sunday. Monsoon
storm chances should persist through at least south-central
Arizona for much of the first half of next week, while humidities
rebound to 20-25% across the lower deserts to upwards of 35-40%
over the eastern Arizona high terrain. Temperatures next week will
remain several degrees above normal each day.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Sunday morning through Monday evening
     for AZZ530.

CA...Excessive Heat Watch from Sunday morning through Monday evening
     for CAZ562-566-567-569-570.

&&

$$

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