858
FXUS65 KPSR 160532
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1032 PM MST Mon Jul 15 2024

.UPDATE...Updated 06z Aviation Discussion.

&&

.SYNOPSIS...
Low level moisture will remain in place through the week supporting
daily thunderstorm chances primarily over higher terrain areas.
Towards the latter half of the week, storm chances will increase
across lower elevations as moisture deepens under a supportive flow
pattern. Temperatures this week will hover in a slightly above
normal range yielding widespread moderate HeatRisk.

&&

.DISCUSSION...
Early afternoon WV imagery and objective analysis depicts the center
of a sub-tropical high situated over northern New Mexico with H5
heights lower (~595dm) than sampled during the entirety of last
week. Concurrently, an elongated upper trough has retrograded into
SW Texas providing impressive jet level divergence throughout
eastern AZ and northern Sonora. These main synoptic features should
remain quasi-stationary over the next 48 hours yielding excellent
upper support for convective development and formation of complexes
with the preferred locations for thunderstorm impacts more modulated
by terrain and mesoscale processes. During the middle of the week,
the aforementioned sub-tropical high will shift westward into
northern Arizona with a tendency towards increasing H5 heights
resulting in modest warming and marginal subsidence. However, by the
weekend, models are in excellent agreement that the high pressure
center continues its westward propagation into Nevada setting the
stage for deeper moisture intrusion, increased widespread storm
activity, and moderating temperatures.

12Z sounding data from KPSR and KTWC sampled a partially overturned
environment from scattered storms and deep outflows last evening,
however a notable E/NE wind trajectory in the H7-H5 layer was in the
process of returning steeper midlevel lapse rates atop 10-12 g/kg
boundary layer mixing ratios. Nevertheless, the preponderance of
model output focuses concentrated storm development over northern
Sonora and far southeast Arizona in a more untouched environment
with propagation towards the pool of higher instability to the W/SW.
More isolated to scattered deep convection is likely over mountains
of northern and eastern Arizona, however HREF output shows just
moderate intensity with only modest outflow generation. As a result,
POPs from the NBM remain rather meager across lower elevations of
south-central Arizona. Elsewhere, moist upslope flow and excellent
upper divergence over SE California will be quite favorable for
storm formation from the mountains of the Baja through central
Riverside County. Similar to yesterday, concerns center around gusty
winds in lower elevations and the potential for storms to anchor
over Joshua Tree National Park producing isolated heavy rainfall.

Although a slight increase in subsidence would be expected with the
high pressure system edging into northern Arizona, moisture will
still be more than sufficient to continue to support afternoon/early
evening storms across the Rim and White mountains through the middle
of the week. However, partial erosion of moisture within and
especially at the top of the boundary layer could reduce mixing
ratios under 10 g/kg which would make lower desert storm sustenance
more difficult. With afternoon DCapes near 2000 J/kg, deep long
traveling outflow boundaries are possible; and it cannot be
discounted that multiple colliding boundaries could invigorate a few
lower elevation storms despite the less than ideal conditions.
Otherwise, as H5 heights rebound slightly, temperatures will respond
by warming back solidly into an above normal category resulting in
widespread moderate HeatRisk, albeit still just short of excessive
criteria. Should the anti-cyclone center and higher heights drift
further south, readings may spike even warmer requiring heat
headlines.

During the latter half of the week and especially into the weekend
with high pressure shifting into Nevada, both the flow pattern and
moisture influx should become very favorable for more expansive
thunderstorm activity. Forecast BUFR soundings suggest boundary
layer mixing ratios returning closer to 11 g/kg with increases total
column PWATs in excess of 1.50". Previous days outflows will likely
deepen the quality moisture depth and the steering flow switch out
of the northeast will become favorable for thunderstorms developing
over the Rim to migrate and survive into the south-central AZ lower
deserts. Details and mesoscale evolutions this far in advance are
impossible to highlight, however at some point in the Friday-Sunday
time frame, a more prolific daily storm environment is likely to
materialize.

&&

.AVIATION...Updated at 1745Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A couple of boundaries are still expected to cause at least one
more wind shift during the early overnight hours. North to
northeast flow will turn southerly over the next hour or two due
to a boundary moving up from the south that should keep winds
south to southwest through 9-11z. Periodic gusts up to 20-25 kts
are possible with this outflow. Otherwise, winds will follow
typical diurnal trends or become variable in the late overnight to
early morning hours. Westerly flow will settle in across the metro
early tomorrow morning, with afternoon gusts 20-25 kts. There is a
potential for another outflow to move across the metro again
tomorrow evening, with a favored direction of east to northeast,
but probabilities are too low to include with this TAF package.
Otherwise, skies will be FEW-SCT for the most part, with higher
terrain convection bringing occasional BKN skies from the east.

Southeast California/Southwest Arizona including KIPL and KBLH:
South/southwest winds will be favored at KBLH with speeds
generally around 13 kt with occasional gusts 20-25 kts. At KIPL,
winds will generally be southeasterly. 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 tomorrow evening, with a very low
chance of outflows reaching either terminal in the evening hours.

&&

.FIRE WEATHER...
Ample moisture will remain in place to support afternoon
thunderstorm development over higher terrain areas of eastern
districts through much of the week with more activity descending
into lower elevations and pushing into western districts towards the
latter half of the week. Gusty, erratic outflow winds will be the
greatest hazard for fire managers with the potential for abrupt wind
shifts to complicate efforts on any current wildfires and new
starts. Otherwise, the general wind pattern will continue to result
in occasional afternoon upslope gustiness of 20-25 mph. Minimum
afternoon humidity levels will generally range between 15-30%
following mostly fair to good overnight recovery of 30-60%.

&&

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

$$

DISCUSSION...18/Lojero
AVIATION...Young
FIRE WEATHER...18