-- Discussion containing changed information from previous version are highlighted. --
352
FXUS65 KPSR 210531
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1031 PM MST Mon May 20 2024

.UPDATE...
-- Changed Discussion --
Updated 06z Aviation Discussion.
-- End Changed 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...
-- Changed Discussion --
Updated at 0530Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds have substantially calmed across all the terminals, now
exhibiting speeds aob 6 kt. Some light, erratic behavior will be
possible through the next several hours before winds definitively
establish out of their typical E/SE drainage directions. Going
forward, wind directions will generally follow diurnal tendencies.
Expect southwest winds to establish by the afternoon across the
terminals with occasional gusts into the mid teens through early
tomorrow evening. Clear skies will prevail through the period,
aside from a thinly scattered deck to the SE based around 8-10 kft
lingering for another hour or so.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns will exist through the next 24 hours
under clear skies. Winds will lessen and turn out of the NW
overnight at KIPL and are expected to pick up again out of the W
tomorrow evening, but with speeds mostly aob 12 kt sustained and
gusts potentially into the low 20s. An extended period of light
wind speeds (aob 6 kt sustained) and variability can be
anticipated at KBLH after southerly winds subside tonight.
-- End Changed Discussion --

&&

.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