424
FXUS65 KPSR 210004
AFDPSR

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

.UPDATE...Updated 00z Aviation Discussion.

&&

.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 0005Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty winds out of the NE associated with an outflow boundary have
reached the terminals late this afternoon. Confidence in the exact
wind directions over the next few hours is low, however, the most
likely evolution will be for these N/E`rly winds to die down over
the next hour or so, potentially going VRB for a time before a
light (aob 10 kt sustained), predominant SW`rly component takes
over through the remainder of the evening. Expect a return to
diurnal tendencies in the wind directions this evening and through
the rest of the TAF period. Confidence is moderate in the typical
E switch occurring as early as 07-09Z at KPHX. FEW-SCT clouds
based at 10-12 kft will clear over the next few hours, and then
clear skies will prevail through at least tomorrow afternoon.

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. Winds will lessen a little bit later 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. Skies will remain mostly clear 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...Whittock
FIRE WEATHER...18