429
FXUS65 KPSR 151429
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
729 AM MST Mon Jul 15 2024

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Monsoonal moisture in place will continue to result in
daily thunderstorm activity for the next several days. Activity
through the first half of the week will be confined mainly to the AZ
high terrain, with chances for the lower deserts increasing once
again by the latter half of the week and through next weekend.
Temperatures throughout the week will remain above normal with
widespread moderate HeatRisk in place.

&&

.DISCUSSION...
A very active evening was observed across the south-central AZ lower
deserts yesterday, including the greater Phoenix metro area, as a
couple of colliding outflow boundaries were enough to overcome
the convective inhibition in place and spark strong thunderstorm
activity. Areas of dense blowing dust, strong to locally damaging
winds, and locally heavy rainfall leading to areas of minor
flooding were all observed. Activity as of midnight has quieted
down across most of the region. Current objective analysis shows
the monsoon high situated over the Four Corners area with
southeasterly flow in place. Thus, moisture levels for today will
not change that much from yesterday. However, given the very
active evening that was observed yesterday, the atmosphere has
been overturned and thus a much quieter day is more likely today
across the south-central AZ lower deserts. This is reflected in
the 00Z HREF guidance, which virtually shows very minimal activity
for later today. Convection is still expected to fire up later
this afternoon along the Rim as well as across portions of
southeast AZ, which could send multiple outflows into the lower
deserts later this evening with a 10-30% chance of gusty winds in
excess of 35 mph. However, given the greater stability that will
be in place from the convective overturning from yesterday`s
activity, these outflows are not expected to be sufficient to
generate additional storm activity across the lower deserts.
Elsewhere, upslope flow is likely to generate a few storms across
northwestern portions of Joshua Tree National Park as well as
along the San Diego Mountains and the northern Baja chain this
afternoon. Activity that develops along the San Diego Mountains
and northern Baja chain could drift into western portions of
Imperial County.

Heading through the middle of the week, the monsoon high is expected
to shift slightly southward towards the Arizona/New Mexico border.
This slight southward shift will lead to increased subsidence
aloft, leading to slightly drier air and lesser instability.
Moisture will still be more than enough to continue to fire up
afternoon/early evening convection across the AZ high terrain, but
given the increased subsidence and lesser instability in place,
very minimal activity is expected across the lower deserts with
outflow winds from the higher terrain activity still capable of
resulting some gusty winds. Heading towards the latter half of the
week and especially next weekend, the center of the high is
expected to reposition north-northwestward towards southern Nevada
with moisture increasing once again as global ensembles show
PWATs rising to above 1.5" across the region. Thus, a more active
monsoon pattern is likely to setup. With the high center
repositioning over southern Nevada, the steering flow will switch
out of the northeast, which will be a favorable trajectory for
thunderstorms that develop over the Rim to migrate into the south-
central AZ lower deserts.

Temperatures this upcoming week will remain above normal but below
excessive heat thresholds with widespread moderate HeatRisk in
place. High temperatures across the lower deserts today and
Tuesday will range between 107-111 degrees and then rise slightly
to between the 110-114 degree range during the middle and latter
half of the week as high pressure slightly strengthens over the
region. Even though extreme heat is unlikely, it will still be hot
enough that the necessary heat precautions should still be taken
if engaging in outdoor activities.

&&

.AVIATION...Updated at 1425Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Current westerly winds will continue into the evening, with some
gusts of 20-25 kt this afternoon and early evening. The atmosphere
is fairly worked over from last nights storms, so no showers are
storms are expected in the Phoenix Metro this evening. However,
storms are still expected to form in the higher terrain to the
north and east of Phoenix, which could push a northeasterly
outflow boundary through the area. At this time, the outflow
boundary is only expected to impact the KDVT and KSDL terminals
between 02/04Z, with gusts of 20-25 kt. Winds will then go light
and variable during the overnight hours, but may predominately be
out of the east. FEW-SCT mid and high level clouds will continue
through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
South/southwest winds will be favored at KBLH with speeds
generally around 12 kt, with some gustiness around 20 kt this
evening. At KIPL, winds will generally be southeasterly, with the
exception of a westerly wind shift from an outflow boundary moving
through this evening. Winds speeds, at KIPL, will generally be aob
10 kt, with gusts up to 25-30 kt for a few hours with the outflow
boundary this evening. FEW-SCT mid and high level clouds will
continue through the TAF period. A few showers/storms that could
migrate off the higher terrain could cause some occasional BKN
high clouds.

&&

.FIRE WEATHER...
Monsoonal moisture will continue to remain in place during the
next several days to result in daily thunderstorm activity,
especially during the afternoon/evening hours. Activity through
the first half of the week will be confined mainly across the AZ
high terrain, with chances for activity for the lower deserts
increasing by the latter half of the week into next weekend. The
biggest thunderstorm hazard will continue to remain outflow winds,
which will result in sudden directional shifts and strong gusts,
exacerbating issues on any ongoing wildfires and new starts.
Otherwise, the general winds will continue to follow diurnal
tendencies with occasional afternoon upslope gustiness of 20-25
mph. MinRHs today will range between 20-30% area wide and fall
slightly into the 15-25% range by the middle of the week with
good overnight recoveries.

&&

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

$$

DISCUSSION...Lojero
AVIATION...Berislavich
FIRE WEATHER...Lojero