935
FXUS65 KPSR 022018
AFDPSR

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


.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 1720Z.

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

No aviation concerns are expected during the TAF period. Winds
over metro Phoenix sites will follow diurnal trends with moments
and variability during directional shifts and occasional afternoon
gusts near 20 kts. Familiar late afternoon/evening breeziness is
likely (>90%) at IPL with gusts 20-25 kts, with daytime gusts near
20 kts expected at BLH. A FEW high clouds will filter in over the
region during the forecast window, but skies will be mostly clear
otherwise.

&&

.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...RW
FIRE WEATHER...Kuhlman