909
FXUS65 KPSR 201109
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
409 AM MST Mon May 20 2024

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
A passing disturbance today will lead to widespread breezy to
locally windy conditions, and even a band of light showers in
South-Central Arizona. The showers will be capable of producing
brief wind gusts in excess of 40 miles per hour, while also
producing very little if anything in the way of rainfall at the
surface. Spring-like conditions, with dry breezy afternoons and
seasonally hot temperatures then prevail through the rest of the
week.

&&

.DISCUSSION...
A low circulation off to the west over the eastern Pacific will
open up into a shortwave trough and quickly slide through the
region today just ahead of another trough moving down the CA
coast. The shortwave will bring breezy to locally windy conditions
today along with a band of elevated showers/virga and "cooler"
temperatures. The wind will be the greatest impact today with
potential for peak wind gusts over 40 mph. The overall surface
gradient winds may peak around 25-35 mph, but a band of elevated
showers in South-Central AZ this afternoon will be capable of
mixing down stronger wind gusts. The last several runs of hi-res
modeling have been supporting the potential for localized wind
gusts up to 40-50 mph associated with the showers. The 00Z HREF
probability of 40+ mph gusts is upwards of 40-50% in Maricopa,
Pinal, and Gila counties. The time period for these showers and
stronger wind potential will likely be brief, with modeling only
showing the higher gusts for up to 2-3 hours. For the greater
Phoenix area this time period looks to be between 1-5 PM. With the
magnitude of wind gusts possible this afternoon, yard decorations,
furniture, etc., disposal bins, and unsecured temporary
structures may be blown around and/or toppled. There is even the
risk shallow-rooted or compromised trees could be knocked down.
There may also be some localized blowing dust this afternoon
depending on land use and open desert areas. While there is no
guarantee winds will get as strong as advertised (momentum
transfer not as strong as modeled), it is still not a bad idea to
take precautions.

As for the western deserts, west of where the band of showers are
expected, peak wind gusts may still reach upwards of 35-40 mph,
especially in favored areas like the Imperial Valley with
downsloping enhancements. The winds out west will also be capable
of kicking up dust and may make for difficult vehicle handling on
roads with crosswinds. Winds across the region should subside
this evening and tonight.

For the band of elevated rain showers this afternoon, the
environmental setup supports most of the rain falling as virga or
a very light shower, with a very dry sub-cloud layer. The
evaporative cooling in this dry layer is what will help with the
generation of the stronger wind gust. So, do not count on seeing
much if any in the way of accumulating rainfall. With that said
however, there will be a very good fetch of moisture into the
region today. Global ensembles even show IVT values as high as
400-500, which would classify as a weak to nearly moderate AR
event. Compared to climatology these IVT magnitude will be near
record levels, granted this the driest time of the year. Still, it
is not out of the question that there could be a little bit more
rain than currently advertised, but rainfall amounts are forecast
to remain under 0.10". The chance for a few lightning strike or
two is not zero with little to no instability in the hail growth
zone, but a little bit of mid-level cooling on the back side of
the band later in the afternoon could present a low chance.

Conditions dry out, with clearing skies, pretty quickly following
the band of showers and conditions are forecast to remain dry for
the next several days. Temperatures will mostly remain seasonal,
which is lower desert highs mostly in the middle 90s, through this
weekend as a general broad troughing pattern persists across the
west. There are indications of at least a couple more embedded
shortwaves, Wednesday and Saturday, within the flow that may lead
to some breezier conditions as well. Overall, typical Spring-like
conditions are expected through the week with dry, low-humidity,
conditions with afternoon breeziness.

&&

.AVIATION...Updated at 1108Z.

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
is likely to push through the Phoenix metro. East winds this
morning will turn westerly fairly early at around 17Z before
increasing and developing gusts into the mid 20s by the afternoon.
Confidence is quite good in virga showers passing over the
terminals during a couple hour timeframe around 21-22Z (coinciding
with the lowest cloud bases), bringing a short period of enhanced
west southwesterly winds upwards of 30-35 kts. Winds will
gradually diminish during the early to mid evening hours after
skies clear late afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation weather concern today will be gusty southwest to
west winds. Occasional gusts will persist at KIPL this morning
before increasing and becoming more consistent by late morning as
gusts begin at KBLH. Gusts will peak during the afternoon hours
between 30-35 kt at both terminals with potential for brief
reductions in visibility from lofted dust. Expect higher clouds
this morning to clear out by the afternoon.

&&

.FIRE WEATHER...
A short-wave trough moving through the region today will generate
widespread breezy to locally windy conditions. Strongest wind
gusts may be generated by a band of high-based showers in South-
Central AZ this afternoon, with 40-50% chance for gusts in excess
of 40 mph, primarily between 1300-1700MST. There may be a brief
period, up to 2-3 hours in eastern districts during the early to
mid afternoon, with critical fire weather conditions. Outside of
shower-generated gusts, widespread wind gusts, across all
districts, up to 25-35 mph are anticipated with some localized
areas like the Imperial Valley seeing up to 35-40 mph. This will
result in widespread elevated fire weather, borderline red flag,
conditions today as minimum RHs fall to 10-15%. Land managers should
be cautious for rapid, uncontrolled spread of any ongoing fires
or new starts Monday.

Following today, typical Spring-like conditions are expected,
with daily afternoon breezes up to 15-25 mph, min RHs between
5-15%, and afternoon high temperatures in the 90s across the lower
deserts. Winds may elevate a little higher than seasonal levels,
and elevated the fire weather conditions, with a couple more
passing waves Wednesday and Saturday.

&&

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

$$

DISCUSSION...Benedict
AVIATION...Kuhlman
FIRE WEATHER...Benedict