802
FXUS65 KPSR 202020
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
120 PM MST Mon May 20 2024

.SYNOPSIS...
After a fast moving weather disturbance clears the region this
evening, dry conditions with temperatures not far from the seasonal
normal will prevail the remainder of the week. As is typical during
late May, gusty winds during the afternoon and early evening hours
will be common across the region.

&&

.DISCUSSION...
Early afternoon WV imagery and objective analysis depicts a compact
negative PV anomaly and subtropical jet segment moving over the
northern Baja in the process of phasing with northern stream energy
deepening towards the Great Basin. This southern shortwave has
entrained a notable plume of moisture with IVT in excess of 500
kg/m/s focused into southern AZ, however the totality of this
advection is occurring above the H7 layer precluding any more than a
few sprinkles/light showers along a decaying cold front through this
evening. Evaporational effects with boundary layer T/Td spreads
exceeding 50F and mechanical momentum transfer associated with
elevated precipitation echoes along the cold front will support
scattered outflows and strong, gusty winds into early this evening
before activity shifts out of the forecast area. Conceptually and
considering past historical cases along with 12Z HREF output, there
is around a 50% chance of 40+ mph gusts later this afternoon around
the Phoenix metro yielding isolated instances of blowing dust (based
largely on nearby land use practices) and significant complications
for ongoing wildfires.

Conditions will dry out quickly with wind speeds gradually weakening
following the frontal passage this evening. Ensemble members remain
in excellent agreement with respect to the overall Conus flow
pattern the remainder of the week highlighted by broad longwave
troughing covering the western half of the United States. With H5
heights trapped in a 576-580dm range across the CWA, forecast
guidance spread is extremely narrow resulting in excellent
confidence of a near persistence forecast throughout the week with
temperatures hovering not far from climatology. Several low
amplitude shortwaves will be embedded in the larger western Conus
cyclonic flow regime, mostly propagating over the Great Basin,
although with a subtle reflection in the southern stream as the jet
configuration still remains partially split. Current indications
suggest Wednesday and Saturday as the best opportunities for modest
height falls associated with the shortwave passage where
afternoon/early evening wind gusts could be enhanced slightly,
albeit with limited impacts.

&&

.AVIATION...Updated at 1815Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation weather concern today will be the potential for
strong gusty winds mid afternoon as a line of mostly virga showers
and some light rain is likely to push through the Phoenix Metro.
West winds will start to gust 20-25 kt around 19Z out ahead of the
approaching cold front. Confidence is good that virga showers and
some light rain showers will form along the cold front that will
move through the Metro between 20-22Z. With this cold front winds
will gust, out of the west/southwest, up around 35 kt, with some
periodic gusts up around 40 kt also possible.

After the cold front and virga/light showers exit the Metro ~22Z,
westerly winds will start to diminish, but stay elevated (25-35 kt)
through sunset. After sunset westerly winds will quickly die off
with speeds around 5-10 kt. Winds will then switch back to the east
during the overnight hours. SCT-BKN clouds with bases aoa 10-12 kft
will quickly clear out this evening behind the cold front.


Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation weather concern today will be gusty southwest to
west winds. Winds at KIPL will predominately be out of the west and
at KBLH will predominately be out of the southwest through the TAF
period. At both terminals current gusts of 20-25 kt will pick up
around 20-21Z with gusts of 30-35 kt. Winds will then lessen a
little bit this evening with gusts going back down to 20-25 kt.
Wind speeds will then lessen even more, down to around 5-10 kt for
the overnight and early morning hours tomorrow. High clouds
currently overhead will clear out this afternoon, with clear skies
for the remainder of the TAF period.

&&

.FIRE WEATHER...
Very typical mid/late May weather will prevail the remainder of the
week highlighted by seasonably warm temperatures, dry conditions,
and frequently breezy afternoon/early evenings. Minimum afternoon
humidity levels will mostly fall into the single digits with some
modest improvement into a 10-20% level towards the end of the week.
This will follow generally poor to fair overnight recovery of 20-
40%. Wind gusts 15-25 mph will be common through the week with some
daily enhancement during the latter half of the week near terrain
features resulting in an elevated fire danger.

&&

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

&&

$$

DISCUSSION...18
AVIATION...Berislavich
FIRE WEATHER...18