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179
FXUS65 KPSR 222003
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
103 PM MST Sat Jun 22 2024

.SYNOPSIS...
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Elevated moisture will continue to result in daily
thunderstorm activity during the next several days, with the highest
chances expected over the higher terrain areas. Temperatures this
weekend will average near to slightly above normal before increasing
some through the middle of next week as high pressure strengthens
over the Desert Southwest.
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&&

.DISCUSSION...
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An elongated ridge of high pressure currently centered across the
Lower Mississippi River Valley is producing a southerly wind flow
across much of the region. This is ushering in higher moisture
content into Arizona with PWATs according to the latest SPC
mesoanalysis ranging between 1.5-1.9" across most of the central
and southern portion of the state. A stream of dense mid to high-
level cloudiness originating from the remnants of former tropical
cyclone Alberto is currently engulfing most of south-central AZ
with the latest MRMS radar data indicating areas of light
showers/virga. This shower activity is being sparked by a weak
inverted trough circulating around the ridge feature at around the
700 mb.

The latest HREF guidance indicates that the cloud cover engulfing
most of south-central AZ will persist through this afternoon and
is adding a layer of complexity in terms of convective potential.
The abundant cloud cover will most likely limit the overall
instability across south-central AZ and thus any thunderstorm
activity is now becoming less likely and this is reflected amongst
the latest hi-res guidance, which has backed off on any robust
convection impacting the area. Nevertheless, with the aid of
orographic lifting and where there has been more surface heating,
thunderstorms are likely to develop along the vicinity of the
Mogollon Rim this afternoon and with the steering expected to be
more out of the east, activity will tend to propagate west to
southwestward, however, given the limited instability storms may
not be able to survive their trip into south-central AZ. Even
though storms may not directly impact the area, outflow
boundaries originating from the activity across the higher terrain
may still be a threat with the latest HREF indicates a 50% chance
of wind gusts in excess of 35+ mph. There is even a low chance
that these outflows may make their way as far west as La Paz and
northern Yuma counties with probabilities of 10-30% of gusts of
35+ mph. There will also be the potential for some blowing dust as
well, especially if these outflows propagate through the dust-
prone areas. With the higher moisture content in place and weak
steering flow, any storms will be capable of localized heavy
rainfall that could result in flooding.

Heading into the Sunday, there will be another inverted trough that
will be moving through. This feature in combination with the
orographic lift will likely spark convection across the higher
terrain areas. Moisture is expected to be even higher, with the
ensembles showing PWATs potentially getting as high as 1.9-2.0",
with forecast model soundings in the Phoenix area showing not much
in the way of convective inhibition due to the more moist
environment. Therefore, any outflows will likely have more success
in initiating new storms even into the lower deserts. With a more
moist environment engulfing all the way westward into southeast
CA, a few storms cannot be ruled out across the western deserts,
especially across Joshua Tree National Park. With the combination
of the moist airmass and very light steering flow, heavy rainfall
resulting in flash flooding will become a greater threat along
with gusty winds.

Heading into next week, the subtropical ridge is expected to
retrograde with 500 mb heights building into the 594-597dm range
by the middle of the next week. Elevated moisture levels will
continue to remain in place and thus daily thunderstorms chances
will persist, with the best chances expected over the higher
terrain areas of eastern AZ. By the latter half of the week, the
ensembles are in very good agreement of a large-scale trough
traversing the Pacific Northwest and Intermountain West. This will
cause the ridge over the Desert Southwest to weaken, with
indications of a drier westerly flow regime setting up, which
would erode somewhat the monsoonal moisture currently in place. As
a result, storm activity would diminish considerably by late next
week if this drier westerly flow regime comes to fruition.

With the cloud cover and higher moisture content in place, temperatures
this weekend across the region are expected to average near to
slightly above normal. Somewhat hotter temperatures are expected
heading into the middle of next week as the subtropical ridge
strengthens over the Desert Southwest. However, with a more moist
air mass in place, latest guidance has backed off on the extreme
temperatures and thus the HeatRisk for the most part is likely to
stay in the moderate category. Even though excessive heat
conditions are looking less likely, temperatures and even humidity
levels will still be high enough that the necessary heat
precautions will still need to be taken, especially if engaging in
outdoor activities. As the ridge weakens by the latter half of
the week, temperatures are likely to cool off slightly.
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&&

.AVIATION...
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Updated at 1750Z.

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

Winds during much of the TAF period are expected to contain an
SE/E`rly component, outside of some brief moments of variability.
Confidence in SHRA and TS activity over terminal locations has
decreased since the last forecast package, but rainfall over or
in the vicinity of TAF sites cannot be completely ruled this
afternoon and evening. The potential of seeing strong outflow
winds associated with convective activity remains but has
decreased, with chances of seeing winds exceed 30 kts now between
30-50% (50-70% 12 hours ago). Potential outflows will be
dependent on where convective development occurs and how
widespread it becomes, and due to the above-mentioned uncertainty,
confidence regarding timing and strength of these features is
low. Future amendments are likely to be needed if more widespread
convection is realized. BKN to occasionally over OVC skies will
prevail through this evening, with the lowest bases around 10k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at IPL are expected to be out of the SE through the TAF
period, with BLH favoring more of a S`rly/SSW`rly component. Both
terminals will see afternoon and early evening gusts between
20-25 kts before winds calm through the nighttime hours. Mostly
clear skies, with a FEW clouds around 10-12k ft, will prevail
through tonight before cloud coverage begins to increase early
Sunday morning.
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&&

.FIRE WEATHER...
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Monsoonal moisture will continue to result in daily chances for
shower and thunderstorm activity, with the best chances for
activity across the higher terrain areas. With the elevated
moisture in place, MinRH values through early next week will
range between 35-45% across the far eastern districts to between
15-25% across the western districts before slowly drying into the
middle to latter half of next week. Winds will follow their
typical daily tendencies, with gusty outflows from any
thunderstorm activity anticipated over the next several days.
Temperatures through the weekend will average near to slightly
above normal before increasing some heading into the middle of
next week.
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&&

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

$$

DISCUSSION...Lojero
AVIATION...RW
FIRE WEATHER...Lojero/Young