410
FXUS65 KPSR 230029
AFDPSR

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

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
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.

&&

.DISCUSSION...
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.

&&

.AVIATION...Updated at 0029Z.

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

Considerable mid and high cloudiness will wax and wane during the
forecast period with ceilings getting as low as FL120 (mainly
tonight into Sunday morning). Due to the cloud cover, instability
is reduced and storms are not expected to develop over the Valley
floor. Storms over Pinal County are anticipated to produce a wind
shift at KIWA early in the TAF period but not nearly as strong as
the past couple of days. Accordingly, the rest of the TAF sites
are anticipated to see an even weaker wind shift to southeasterly.
A weaker though larger outflow from the east will also aid in the
onset of easterly surface winds. Prior to that point, surface
winds will be highly variable across the metro area with speeds
AOB 12kts but mainly below 8kts. One other scenario that could
play out with winds this evening is outflow from storms currently
over Yavapai County and the Rim north of Payson pushing south into
the metro area. Confidence in that scenario is too low to reflect
in the TAFs at this time. Winds during the day Sunday are expected
to continue to be light and eventually favor westerly in the late
afternoon. A good deal of uncertainty remains on how thunderstorm
activity will develop Sunday afternoon. Confidence too low at this
time to reflect thunderstorm related impacts in the TAFs.


Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at IPL are expected to be out of the SE through the TAF
period with speeds waning tonight and then picking up during the
day. At KBLH, directions will favor south and southwest this
evening before becoming light and variable overnight favoring
drainage patterns. Southerly breeziness (gusts 20-25kts) resumes
during the day Sunday. As for sky cover, FEW cumulus will decrease
this evening but cirrus will increase tonight and linger through
Sunday.


&&

.FIRE WEATHER...
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.

&&

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

$$

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