536
FXUS65 KPSR 300616
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1116 PM MST Sat Jun 29 2024

.UPDATE...
06Z Aviation Discussion.

&&

.SYNOPSIS...
Above normal temperatures will persist into next week, especially
for the western deserts, where daily highs are expected to be
near or above 110 degrees. Shower and thunderstorm activity will
be limited today before becoming more widespread over south-
central Arizona by Sunday. Enhanced monsoonal moisture will keep
rain chances elevated through at least the middle of next week,
with the best chances focused over high terrain areas north and
east of the Phoenix metro.

&&

.DISCUSSION...
Current WV analysis reveals a sharp contrast in the environment
between each end of our forecast area, with very dry conditons being
observed over Southeast California, while parts of south-central
Arizona have seen better moisture that lead to some light showers
this morning. Meanwhile, the sub-tropical ridge has now become
centered over the Southern Plains, which will help to keep
favorable monsoonal flow over the region through this weekend.
However, the ridge will strengthen through the day today,
stretching out over the Desert Southwest once again. This will
provide renewed subsidence aloft, which should limit convective
activity for most of our CWA this afternoon and evening.
Nonetheless, with the relatively enhanced moisture profile (PWATs
1.3-1.5") over much of southern Arizona, it is not out of the
question that areas in Pinal, Gila, and southern Maricopa Counties
see terrain influenced convection once the atmosphere starts to
destabilize this afternoon. If storms do initiate, the environment
will be be favorable to see some enhanced to potentially damaging
downbursts with stronger storms.

As mentioned in previous discussions, an easterly wave, currently
seen in WV imagery over northern Mexico, will advance towards the
Desert Southwest through tonight, helping to turn our mid-level flow
toward the southeast, providing increased moisture flux over the
region. This wave will also help to spark an MCS over Sonora later
today, which may play in part in setting off some elevated
showers over southeastern and south-central Arizona Sunday morning
due to additional moisture advection and any associated gravity
waves.

Model guidance has shown a consistent signal regarding Sunday
being an active monsoon day across parts of Arizona. The dynamics
associated with the above-mentioned easterly wave will tap into
what will be a relatively unstable environment (MUCAPE 500-1000
J/kg) over southeast Arizona and up through Gila County Sunday
afternoon. Hi-res data has convection developing near the Tucson
area during the afternoon hours, before advancing towards Pinal
and Maricopa Counties Sunday evening. The environment over the
Phoenix metro and down along the I-10 corridor will be slightly
more stable, but would still support further convective
development, with MUCAPE values between 500-750 J/kg. Model
soundings do point toward at least some CIN being present, but
strong outflows from the previously-mentioned activity should
provide enough lift to overcome this capping, likely sparking
further thunderstorm initiation. Best chances to see shower and
thunderstorm activity over our CWA will be focused over the high
terrain areas north and east of Phoenix, where a greater axis of
instability will be present, with current Pops between 60-80%.
Closer to the Phoenix metro, rain chances range between 30-40%,
likely due to the slightly lower instability, and greater
projected CIN. Nonetheless, even with these more subdued rain
chances, there is good confidence that areas around the metro will
see activity. Some storms are likely to be strong to severe with,
damaging winds possible. Stronger outflows will also have a high
potential of generating areas of blowing dust, especially across
the usual dust prone areas in Pinal County. With ample moisture
available, heavy rainfall, with potentially minor flooding, will
also be potential hazard with Sunday`s activity. One potential
limiting factor to all of this will be lingering cloud cover from
tonight`s storms over northern Mexico, with models hinting at
decent cloud cover over south-central Arizona through Sunday
morning. If these were to stick around into the afternoon hours,
it could limit convective activity and coverage due to more
limited insolation. However, models seem to agree that clearing
should take place by late morning/early afternoon, favoring a more
active solution.

The GFS continues to show the development of and MCV over south-
central Arizona late Sunday. This feature will drift of towards
Flagstaff on Monday, leaving a good portion of our CWA under the
influence of subsidence, likely limiting shower and thunderstorm
development, at least over the lower-elevations, Monday afternoon
and evening. Regional flow will also shift out of the southwest
during the start of the week, providing some slight drying,
creating another inhibiting factor for more widespread
thunderstorm activity. Nonetheless, terrain driven convection
looks likely as moisture levels remain above normal, with current
PoPs over northern Maricopa and southern Gila Counties ranging
between 40-70%. Forecast confidence for Tuesday and Wednesday is
still somewhat low due to the lack of any good forcing as we will
fall in between a developing high pressure ridge off the coast of
California and the ridge center over the Lower Mississippi Valley.
A couple of weak upper level shortwave troughs are also expected
to pass by to our north Tuesday and Wednesday with potentially a
little bit of upper level forcing over Arizona on Wednesday. This
may help with some convection, but a southwesterly steering flow
is generally not very favorable for convection impacting the lower
deserts. Even with this level uncertainty, NBM shows PoPs over
Gila County upwards of 50-60% through Wednesday, so daily terrain-
driven convection is still possible through mid-week. By late
next week, the aforementioned Pacific high will move onshore,
shifting flow over the Desert Southwest out of the north,
resulting in further drying, which would limit monsoon activity
though at least next weekend.

Temperatures during the next seven days will continue to exceed
seasonal-normals, especially out in the deserts of southeastern
California. Daily readings across south-central Arizona will range
between 104-112 degrees, while temperatures near and above 110
degrees will be common further west. These temperatures, combined
with expected dew points in the 50s, will result in in widespread
Moderate, to locally Major, HeatRisk. In response, the Excessive
Heat Watch for parts of southeast California has now been upgraded
to a warning and will be in effect through the end of the upcoming
work-week.

&&

.AVIATION...Updated at 0600Z.

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

A batch of showers and storms will traverse across southern AZ
overnight. Rain chances will remain low (<20%) at the metro
terminals through sunrise Sunday morning. Winds will follow
typical diurnal tendencies with easterly flow becoming established
by 07Z at KIWA and 09Z at KPHX tonight followed by an early
westerly shift Sunday morning. Gusts into the teens will be
possible Sunday afternoon. Skies will remain partly cloudy with
bases SCT 8-10 kft and BKN 20-25 kft.

By tomorrow evening, there is a high chance (>70%) of an outflow
boundary arriving from the S-SE. Timing and strength of the
outflow is still a bit uncertain, but there will likely be an
abrupt wind shift accompanied by gusts reaching 20-30 kts and
potential for blowing dust. There is also a 30% chance of TSRA at
all terminals tomorrow night, mainly after 03Z. We will continue
to adjust arrival time of the outflow and possible TSRA in
subsequent forecasts.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are anticipated through the forecast period.
Winds will continue to follow their typical diurnal patterns
with a westerly flow continuing at KIPL and southwesterly flow
persisting at KBLH overnight. Speeds should generally remain 8
kts or less. There will likely be wind shift out of the S-SE
Sunday morning as decaying showers near the Colorado River Valley
send an outflow boundary through the region. Elevated winds will
continue through the afternoon with gusts up to 20 kts possible at
KBLH. Skies will remain mostly clear through the TAF period.

&&

.FIRE WEATHER...
Very limited monsoon activity is expected today before fairly
widespread showers and thunderstorms are expected over south-
central and eastern Arizona Sunday afternoon and evening. Humidity
levels today will drop slightly from yesterday with MinRHs in the
upper teens across the lower deserts to 20-30% over the higher
terrain with only very slight improvement through Sunday
afternoon. Overnight recoveries will be fair tonight and good
Sunday night as moisture increases over much of the area. Winds
will follow typical diurnal trends through Sunday afternoon with
occasional afternoon breeziness near 20 mph, while strong outflow
south southeasterly winds look likely Sunday evening into south-
central Arizona. Daily monsoon storm chances should persist
through at least south-central Arizona into the middle part 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 Warning from 10 AM Sunday to 8 PM MST Friday for
     AZZ530.

CA...Excessive Heat Warning from 10 AM Sunday to 8 PM PDT Friday for
     CAZ562-566-567-569-570.

&&

$$

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