134
FXUS65 KPSR 160004
AFDPSR

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

.UPDATE...Updated 00z 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:
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 or
storms are expected in the Phoenix Metro this evening. However,
some isolated storms are still expected to form in the higher
terrain to the north and east of Phoenix which could push a
northeasterly outflow boundary into the Valley. At this time, the
outflow boundary is trending towards more likely to impact SDL,
DVT, and possibly IWA, with a TEMPO added for a E-NE winds gusting
20-25 kts between 04-06z. Depending on the exact timing of this
gulf surge and the aforementioned outflow boundary, the gulf surge
may dominate and keep the outflow out of KDVT and KSDL. Winds
will then go light and variable during the overnight hours, but
may predominately be out of the east before switching back
westerly by the mid-to-late morning timeframe tomorrow. 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 13 kt with occasional gusts 20-25 kts. No outflow
boundary is anticipated to reach KBLH that would cause any concern
about any abrupt wind shifts at this time. At KIPL, winds will
generally be southeasterly, with the exception of a westerly wind
shift from weak sundowner winds. 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 this evening.

&&

.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/Berislavich
FIRE WEATHER...18