683
FXUS65 KPSR 151206
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
506 AM MST Wed May 15 2024

.UPDATE...Updated 12Z Aviation Discussion.

&&

.SYNOPSIS...
Above normal temperatures will continue through at least the
weekend with lower desert highs warming from the mid to upper 90s
today and Thursday to just over 100 degrees on Saturday. Typical
late afternoon and early evening breeziness along with mainly dry
conditions will persist. Isolated afternoon shower and
thunderstorm activity will occur over the high country through
Thursday, which could cause some erratic, gusty winds that could
make their way into the Valley each evening.

&&

.DISCUSSION...
A weak upper level low is currently situated just off the coast
of southern California, while moisture levels have increased to
slightly above normal across much of the region. Although moisture
has increased over the region, the bulk of the moisture is above
12K feet which is not uncommon for a springtime weather system.
High-based high terrain showers and isolated thunderstorms are
again expected today across the northern half of Arizona and
potentially as far west San Bernardino County in California. The
positioning of the upper level low today will generally result in
a northeasterly steering flow potentially pushing any decaying
higher terrain convective activity into northwestern Maricopa and
La Paz Counties. Although we do not anticipate any of this
activity to bring measurable rainfall to our area, it has a
greater than 30% probability of bringing 35 mph or greater
outflow winds into the aforementioned areas. The Phoenix area
could also get some outflow winds this evening, but HREF
probabilities are generally closer to 10% for 35+ mph winds.

As the center of the upper low tracks along the Arizona/Mexico
border this evening and tonight, another shortwave trough is
forecast to quickly dive southward into Arizona out of Utah.
Forecast soundings during the overnight hours tonight still
support weak mid-level instability, while the steering flow turns
north northwesterly. Latest CAMs show potential for some high-
based showers tracking into south-central Arizona, including the
Phoenix area during the overnight hours, but given the very dry
sub-cloud layer in place measurable rainfall is at most only a 5%
probability.

For Thursday, the threat for high-based showers and isolated
thunderstorms will shift more over eastern Arizona with the CAMs
showing convection firing along the Mogollon Rim in the
afternoon. With a northwesterly steering flow, this activity is
likely to make it into southern Gila County later in the afternoon
with even a 5-10% chance of an isolated shower into northeastern
Maricopa County. The high-based convection will again promote
gusty outflow winds with the HREF showing over a 50% probability
of 35 mph or greater winds just to the east of Phoenix and even a
30-50% probability across the Phoenix metro.

Temperatures over the next couple days will be slightly cooler
than the past couple days, but still a few degrees above normal
as the weak upper level low affects the region. Starting Friday,
upper level ridging will again move into the region leading to
drier conditions and warming temperatures. Forecast highs on
Friday show readings right around 100 degrees across the majority
of the lower deserts. As the ridge fully moves over the region
this weekend, H5 heights will rise to between 582-585dm and highs
are expected to peak on Saturday with readings between 100-103
degrees. This will put a good portion of the lower deserts within
the Moderate HeatRisk category. Ensemble guidance is in good
agreement showing another weak closed low approaching northern
Baja by Sunday, while a larger upper level trough begins to dig
southeastward across the Northwestern U.S. Guidance then shows
the closed low weakening and likely getting absorbed into the
upper low which should continue to dig southward over the Western
U.S. As the trough is favored to shift into the region on Monday,
temperatures will begin to cool off a bit allowing highs to drop
back into the 90s. As of right now, there is little indication of
much in the way of moisture or rain chances with the system for
early next week. The highest the NBM PoPs reach is 10-15% in far
northeast Arizona on Monday with near 0% chances persisting over
the lower deserts.

&&

.AVIATION...Updated at 1200Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary aviation weather concern through the TAF period will
be the potential for gusty northerly outflows reaching the
terminals this evening, as convective activity is expected over
the high terrain to the north. KDVT and KSDL have the best chance
(30-40%) of seeing gusty winds of around 25-30 kt between 03-05Z
this evening. Confidence is lower at KPHX (10-20%) as any outflow
boundary will weaken as it moves further south. But there may be
brief gusty winds around 20 kt between 04-05Z this evening at
KPHX. Confidence in an outflow boundary reaching KIWA is the
lowest at this time (< 10%). Apart from any outflow boundaries
reaching the terminals, wind directions will follow their typical
diurnal tendencies, with sustained speeds mostly aob 10 kt and
gusts into the mid-to-upper teens developing this afternoon. Thin,
widely scattered cloud layers aoa 10-12 kft can be anticipated at
times through this afternoon before mid and high level clouds move
over the region during the overnight hours becoming BKN around 20
kft at times.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are anticipated through the
next 24 hours. Winds will favor a westerly component through much
of the TAF period at KIPL, with speeds generally aob 7 kt through
the early evening. Wind gusts, at KIPL, will redevelop up to
around 20 kt this evening and then once again subside during the
overnight hours. At KBLH, winds will maintain a SW to S component
through most of the period, with occasional gusts around 15-20 kts
late this evening. Mostly clear skies with some passing mid to
high level clouds at times will continue.

&&

.FIRE WEATHER...
Weather conditions will be a bit more active through Thursday
with enough moisture over the higher terrain for afternoon high-
based shower and isolated thunderstorm activity. This activity may
result in gusty outflow winds tracking southward into northern
portions of Maricopa and La Paz counties this evening and over
Maricopa and Gila counties late Thursday afternoon/early evening.
With MinRHs down to between 10-15% both days and dry fine fuels in
place, the potential for outflow winds will create an elevated
fire danger. Gradient winds on Thursday are also expected to
increase with widespread afternoon gusts to around 20 mph. Drier
and warmer conditions are then anticipated Friday and through the
weekend as high pressure slowly moves through the region. This
will result in continued elevated fire weather conditions each day
with MinRHs between 5-10%, high temperatures 5-10 degrees above
normal, and breezy daytime conditions.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Berislavich/Whittock
FIRE WEATHER...Kuhlman