535
FXUS65 KPSR 022305
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
405 PM MST Sun Jun 2 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Slightly above normal temperatures are expected through Tuesday
before high pressure builds across the western United States,
resulting in hotter temperatures during the middle to latter
portions of the upcoming week. Excessive Heat Watches are in effect
Wednesday and Thursday across most of south-central AZ as well as
for portions of Riverside and Imperial Counties in southeast CA as
high temperatures approach 110 degrees. Cooler temperatures are then
expected by next weekend as a weak disturbance moves across the
region.

&&

.DISCUSSION...
The overall weather pattern continues to remain similar to what has
been observed during the past several days with the Desert Southwest
remaining in between the sub-tropical high over Mexico and cyclonic
flow over the northwestern U.S. through southwest Canada. This will
continue to result in a dry, quasi-zonal flow through Tuesday. As a
result, temperatures will remain nearly unchanged as highs will
range between 100-105 degrees across the lower deserts, which is
just slightly above normal for this time of the year.

By later Tuesday into Wednesday, the overall synoptic pattern will
undergo a significant change as the sub-tropical ridge off the
eastern Pacific will be amplifying across the majority of the
western U.S., while simultaneously a cutoff upper-level low will
develop and sit off the central Baja Peninsula. With the amplifying
ridge, 500 mb height fields are forecast to rise from the current
582-585dm to 589-593dm beginning on Wednesday, resulting in hotter
temperatures. The latest NBM guidance shows highs over the lower
deserts on Wednesday between 106-110 degrees, increasing a couple of
degrees further on Thursday to between 108-112 degrees. The
forecasted high for Phoenix Sky Harbor for Thursday is currently
sitting at 112 degrees, which if it would come to fruition, would
break a daily record high of 111 degrees last set in 2016. Given the
increasing temperatures during the middle to latter portions of the
week, the overall HeatRisk will be elevated to moderate areawide
with areas of Major Heatrisk materializing, especially across south-
central AZ as well as across portions of eastern Riverside and
western Imperial Counties in southeast CA. As a result, an Excessive
Heat Watch is in effect for these areas for Wednesday and Thursday.

The aforementioned upper-level low off the Baja Peninsula is
expected to eventually make its way northward through our region
heading into next weekend. However, the latest guidance has trended
slower with progression of this feature into our region in the last
couple of iterations and thus it is appearing more likely that the
ridge will still be in full control through Friday, resulting in the
continuation of excessive heat conditions. This overall trend is
being reflected in latest NBM guidance, which is a couple of degrees
warmer with highs ranging between 106-111 degrees across the lower
deserts. Thus, it is very possible that the current Excessive Heat
Watches in effect may very well extend through Friday.

By next weekend, as the upper-level low finally migrates through the
region, temperatures will be on cooling trend with highs retreating
back to near normal, between 100-105 degrees across the lower
deserts. Moisture advection from the progression of the upper-level
low northward will likely result in PWAT values to rise to around
150-175% of normal, which may be enough to spark some afternoon
convection across the eastern AZ high terrain, where the NBM
currently has slight PoPs.

&&

.AVIATION...Updated at 2305Z.

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

No major weather concerns will exist through Monday evening under
clear skies. Across the Phoenix metro, aside from a few westerly
gusts 15-20kt through early evening, wind behavior and timing of
typical wind shifts will be very similar to the past several days.
In SE California, a period of gusty sundowner winds around 25kt
should affect KIPL through mid evening with remnant afternoon gusts
20-25kt relaxing at KBLH by mid evening.

&&

.FIRE WEATHER...
Little to no change in the weather pattern will keep seasonably dry
and hot conditions in place through Tuesday. Expect 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% over the
eastern districts to 35-50% over the western districts. Winds will
remain fairly light following diurnal tendencies with periodic
afternoon gusts of 15-20 mph. The latter half of the week will see
even hotter temperatures with potential for highs around 110 degrees
Wednesday through Friday over portions of the lower deserts. There
will also eventually be a slight improvement in humidities by next
weekend along with a low end chance of some isolated thunderstorms
over the Arizona higher terrain.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Wednesday morning through Thursday
     evening for AZZ534-537>546-548>555-559>562.

CA...Excessive Heat Watch from Wednesday morning through Thursday
     evening for CAZ563-566-567-570.

&&

$$

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