021
FXUS65 KPSR 312306
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
405 PM MST Fri May 31 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Seasonably hot and dry weather conditions will persist through early
next week with temperatures running 3 to 5 degrees above normal. By
the middle through latter half of next week, high pressure is
forecast to strengthen across much of the western United States,
resulting in hotter temperatures as high get closer to 110 degrees
across much of the lower deserts.

&&

.DISCUSSION...
A mostly quasi-zonal flow pattern is persisting across the Desert
Southwest as the region is entrenched between the subtropical ridge
located over central Mexico and cyclonic flow near the Canadian
border as well as the Pacific Northwest. This overall pattern is
expected to persist into early next week, with temperatures
remaining steady state with highs between 100-105 degrees across the
lower deserts, which is a good 3-5 degrees above normal for this
time of the year. This will continue to result in widespread minor
HeatRisk with pockets of moderate HeatRisk. A very weak shortwave
trough will bypass just to the north Sunday, however, it will have
no discernible sensible weather impacts other than maybe slightly
enhance the afternoon breeziness.

Heading into the Tuesday-Wednesday timeframe, the weather pattern
will be changing as a ridge of high pressure will amplify across
much of the western U.S while a weak upper-level low develops off
the Baja California Peninsula. In consequence, in response to the
amplifying ridge pattern, 500 mb height fields across the region
will be rising to between 588-594dm heading into the latter half of
next week. This will translate to hotter temperatures with highs
ranging between 105-110 degrees across the majority of the lower
deserts from next Wednesday through Friday. These hotter
temperatures will elevate the HeatRisk into the moderate category
across the majority of the area.

Even though there is high confidence of a strong ridge developing
across the majority of the western CONUS heading into the middle to
latter half of next week, the evolution of the aforementioned upper-
level low off the Baja Peninsula is a bit more uncertain as model
guidance differs in the overall positioning and whether or not this
feature will eventually move into our region. At this time, GEFS
seems to be the most aggressive in moving this upper low into our
region while both the Canadian and ECMWF ensembles are not as
aggressive. This overall evolution will determine whether or not the
region sees a slight cooling trend with highs in the low to mid 100s
or readings remaining near 110 degrees heading into next weekend.
This uncertainty is being reflected in the NBM inter-quartile
temperature distribution, which shows as high as an 8 degree spread
between the 25th and 75th percentile heading into next weekend. With
the upper-level low being positioned near the Baja Peninsula, south
to southeast flow along the east side of the low will likely advect
some moisture into the region late next week through next weekend,
just enough to cause an increase in cloud cover and maybe some
isolated weak afternoon convection across the AZ high terrain.

&&

.AVIATION...Updated at 2305Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation issues will exist through Saturday evening under clear
skies. Wind trends across the region should be nearly identical to
the past 24 hours with a higher probability of gusts 15-20 mph at
the Phoenix area terminal Saturday afternoon. Extended periods of
variable directions and/or nearly calm conditions can be expected
for SE California terminals.

&&

.FIRE WEATHER...
Hot and dry conditions will persist into next week with lower desert
highs between 100 and 105 degrees, or 3-5 degrees above average each
day. MinRH values will continue to run between 5-10% across the
majority of the area each day, while overnight recoveries will
continue to range from poor to fair at around 25-40%. Winds will
overall be fairly light following diurnal tendencies with periodic
afternoon gusts of 15-20 mph.

&&

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

&&

$$

DISCUSSION...Lojero
AVIATION...18
FIRE WEATHER...Kuhlman