155
FXUS65 KPSR 290013
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
513 PM MST Fri Jun 28 2024

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
Above normal temperatures will persist well into next week, with
many lower desert locations seeing highs near or exceed 110
degrees each afternoon. Sunday looks to be the hottest over the
next week, resulting in an Excessive Heat Watch for portions of
Southeast California starting Sunday. Minimal monsoonal rainfall
is expected through the start of the weekend, with only slight
chances for an isolated shower or thunderstorm for areas east and
southeast of Phoenix. Moisture and subsequent rain chances will
increase starting Sunday, likely lasting through the middle of
next week.

&&

.DISCUSSION...
Current atmospheric analysis continues to show the sub-tropical
ridge stretched out over parts of Southern Arizona and Northern
Mexico, while a compact area of low pressure moves over the Northern
Plains and Southern Canada. In between these two systems, westerly
flow aloft will prevail through today before becoming more southerly
by Saturday as the center of ridge becomes established over the
Southern Plains. This high pressure is also expected to strengthen
over the weekend, resulting in increasing heights aloft and a
concurrent rise in temperatures. Day-to-day highs will increase
about a degree a day, maxing out between 110-114 degrees by Sunday
across the lower deserts.

The westerly flow will continue to funnel dry air towards the Desert
Southwest through the remainder of today, especially aloft, where a
noticeable dry pocket was observed between 500-300mb in this
mornings Phoenix sounding. However, enhanced boundary layer moisture
is expected to stick around for longer than originally forecasted,
which could play into shower and thunderstorm potential this
afternoon and evening for south-central Arizona. Subsidence aloft
provided by the aforementioned ridge has been one of the main
limiting factors for monsoon activity over the past few days but
with the high starting to retreat to the east today, this subsidence
may not be as much of a factor. As a result, hi-res guidance is now
hinting at the potential for some isolated shower and thunderstorm
activity across parts of south-central Arizona this afternoon and
this evening. With forecast soundings projecting DCAPE values this
afternoon exceeding 1600 J/kg, enhanced wind gusts cannot be
completely ruled out with stronger cells.

By Saturday, as the sub-tropical ridge becomes established over the
Southern Plains, flow across Arizona will become more southerly to
southeasterly, allowing for continued moisture flux over the state.
At the same time, an easterly wave will traverse northern Mexico,
eventually making its way toward southeast Arizona by late
Saturday/early Sunday. The dynamics associated with this wave,
combined with PWAT values between 1.5-1.75", should create a
favorable environment for potentially widespread shower and
thunderstorm activity across south-central Arizona. NBM PoPs have
trended downward, mostly for lower elevation area, since the
previous forecast update. However, given the favorable setup, it
appears that rain chances are being underdone at this time. One
potential factor that may inhibit convection during this timeframe
will be the presence of cloud cover, with greater coverage likely
resulting in less thunderstorm activity. The main uncertainty
appears to be how long these clouds may stick around for, but we
should have a better idea of how things will evolve during the
next 12-24 hours.

The overall pattern will remain favorable for monsoon activity
through at least the middle of next week as the ridge over the
Southern Plains remains mostly stationary. At the same time, an
anomalously strong ridge will develop over the eastern Pacific,
eventually moving onshore by late next next week. Based on where the
models position this feature, dry northerly flow would likely take
over, limiting further rain chances, while temperatures potentially
climb toward the 115 degree mark for areas across the lower
deserts.

&&

.AVIATION...Updated at 0013Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

SW/Wly flow is in place through the troposphere but with Wly/NWly
at the surface. Winds early in the TAF period will have some
gustiness of 20-25kts before slowly weakening. A potential "fly-
in-the-ointment" would be thunderstorm outflow winds. There is a
10-30% chance of a thunderstorm developing near Casa Grande and
and/or City of Maricopa which in turn would likely produce
sufficient outflow to cause some sort of wind shift at KPHX and
KIWA (less likely at KSDL and KDVT). Elsewhere, storm activity
over/near Tucson will likely produce some outflow that pushes into
Pinal County with a about a 10-30% chance of causing a wind shift
at KIWA (less likely at the other TAF sites). Apart from outflows,
anticipate winds to slowly trend to familiar nocturnal directions
after about 08Z. Expect southwesterly winds to redevelop in the
afternoon Saturday. As for sky cover, anticipate a batch of
remnant/leftover clouds (bases AOA FL150 and mainly cirrus level)
from decayed storms over southeast AZ and NW Mexico to waft over
the Valley late tonight and Saturday morning before thinning out.


Southeast California/Southwest Arizona including KIPL and KBLH:

Overall, expect familiar warm season wind patterns at the TAF
sites through Saturday. At KIPL, westerly winds (gusts of 20-25kts
at times) will be favored this evening before shifting to
southeasterly by sunrise. At KBLH, SWly breeziness (gusts
20-25kts) can be expected early in the TAF period before weakening
and then trending to southerly late tonight. Southerly breeziness
(gusts to 25kts) resumes around midday Saturday. Otherwise, expect
clear skies.

&&

.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 Friday evening
     for AZZ530.

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

&&

$$

DISCUSSION...Kuhlman/RW
AVIATION...AJ
FIRE WEATHER...Kuhlman