546
FXUS65 KPSR 161204
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
504 AM MST Tue Jul 16 2024

.UPDATE...Updated 12z Aviation Discussion.

&&

.SYNOPSIS...
Sufficient moisture will remain in place through the next several
days supporting daily thunderstorm chances, mainly over the
higher terrain areas. By the end of this week and through the
weekend, storm chances will increase across the lower deserts as
moisture increases. Temperatures will continue to remain above
normal yielding widespread moderate HeatRisk, with areas of major
HeatRisk potentially developing during the Friday-Saturday time
frame.

&&

.DISCUSSION...
Latest water vapor satellite imagery as well as objective analysis
depict the center of the subtropical high over northern New
Mexico. During the next couple of days the high will slowly
migrate westward into Arizona. As it does so, it will lead to
some slight drying under increased subsidence aloft. Despite this,
sufficient moisture will still be in place to result in daily
thunderstorm activity across the AZ high terrain. Across the lower
elevations, thunderstorm activity through the middle of the week
will be hard to come by as the increased drying and subsidence
will lead to marginal instability and significant convective
inhibition. Thus, any storms that descend into the lower deserts
from the higher terrain will likely weaken. However, with DCAPE
values still expected to range between 1500-2000 J/KG, the
environment will be favorable for deep long traveling outflow
boundaries, which could impact the lower elevations with gusty
winds.

Heading towards the latter half of the week and especially during
the upcoming weekend, the subtropical high will be shifting into
Nevada with moisture increasing as global ensembles indicate PWATs
rising above 1.5". Thus, a more active monsoon pattern is likely
to setup. NBM PoPs for the lower deserts of south-central AZ
increase to above 20% starting on Thursday. The overall synoptic
pattern for more widespread thunderstorm activity becomes more
favorable heading into the weekend and early next week as a
diffluent flow aloft pattern looks to be setting up due to the
subtropical high positioning across Nevada and an upper trough
diving into the Plains. This more favorable synoptic pattern setup
is being reflected in the latest NBM guidance, which shows
elevated PoPs upwards of 40-50% for both Sunday and Monday across
the lower deserts of south-central AZ. With the overall steering
flow establishing out of the northeast, the trajectory will be
favorable for storms that develop over the Rim to migrate and
survive into the south-central AZ lower deserts. Historically,
northeasterly flow events have lead to severe weather materializing
across the Phoenix area so this is something that bears watching
as we get closer to the weekend once the overall mesoscale details
become clearer.

As the center of the subtropical high shifts westward through
Arizona and into southern Nevada through end of the week and into
the upcoming weekend, 500 mb height fields will slightly rise and
thus surface temperatures will gradually warm up as well. High
temperatures through Thursday will range between 108-113 degrees
across the lower deserts but then could get closer to 115 degrees
across many areas during the Friday-Saturday time frame.
Widespread moderate HeatRisk is expected through Thursday, however
by Friday and Saturday as temperatures warm closer to 115 degrees,
areas of major HeatRisk look to materialize and thus excessive
heat products may be needed. The good news is that a slight
cooling trend is likely starting on Sunday.

&&

.AVIATION...Updated at 1205Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation weather concern through the TAF period will
be the potential for sudden wind shifts associated with any
outflow boundaries that reach the terminals this evening.
Confidence is low on exact wind directions between 02-07Z as a
result of the boundaries that are expected to push through
portions of the Greater Phoenix Area. The first boundary will
likely come out of the ENE, has the best chances of reaching
KSDL/KDVT, and the shift in direction is expected to be temporary
and return to S-SW later in the evening. A second boundary is also
present in the latest Hi-Res guidance emanating from distant
storms to the south southeast and is expected to reach KIWA
sometime between 05-07Z. Outside of any complicating outflows,
winds will follow typical diurnal tendencies for this time of
year, with westerly gusts up to 20-25 kt developing by this
afternoon. Skies will be FEW-SCT and occasionally BKN this
evening/overnight with cloud bases remaining aoa 10 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
There are no major aviation weather concerns through the next 24
hours under FEW-SCT mid and high level clouds. SE wind directions
will be favored at KIPL through the TAF period except this
evening, where westerly winds are expected to prevail. KIPL could
see some westerly gusts up to around 20 kt this evening, and there
is around a 10% chance that a westerly outflow could make it to
the terminal from isolated convection over the mountains to the
west southwest late this afternoon. Winds will favor SSW through
the period at KBLH with gusts up to 20-25 kt at times.

&&

.FIRE WEATHER...
Sufficient moisture will remain in place to result in daily
thunderstorm activity through the next several days. Activity
will be confined mainly to the AZ high terrain through midweek,
with chances expanding into the lower elevations by the latter
half of the week and through the upcoming weekend. Gusty, erratic
winds will be the biggest hazard with these thunderstorms,
exacerbating issues on any ongoing wildfires and new starts. Aside
from the thunderstorm winds, the typical afternoon upslope
gustiness upwards of 20-25 mph will be common. MinRHs during the
next several days will range between 15-30% with fair to good
overnight recoveries between 30-60%.

&&

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

$$

DISCUSSION...Lojero
AVIATION...Whittock
FIRE WEATHER...Lojero