344
FXUS65 KPSR 072151
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
251 PM MST Fri Jun 7 2024

.SYNOPSIS...
Continued high pressure over the region will lead to well above
normal high temperatures again this afternoon. As a result,
Excessive Heat Warnings remain in effect through this evening. A
weak disturbance will pass over the Desert Southwest this weekend,
leading to increased cloud cover and slightly cooler temperatures
into early next week. Temperatures heat up again for the middle of
next week as high pressure builds over the region.

&&

.DISCUSSION...
A weak upper level low has remained nearly stationary off the Baja
Peninsula for the last 24 hours, with a broad ridge downstream over
the Southwest US, allowing for continued southerly to southeasterly
flow over southern AZ. As abundant mid-level moisture was already
present over the region, convective activity began quite early today
over the high terrain of eastern AZ and western New Mexico. Very low
(less than 10%) chances for an isolated dry thunderstorm remain over
eastern Gila County through the remainder of today. The
aforementioned ridging in place overhead will continue to bring us
temperatures in excess of 110 degrees for some lower desert
locations this afternoon. Pockets of Major Heatrisk coinciding with
these hotter locations still remain today, and so Excessive Heat
Warnings will continue to be in effect through 8 pm MST this
evening.

Over the next 24-36 hours, the cutoff low that has been sitting west
of the Baja Peninsula will move northward and eventually cross into
southern AZ. As this is a relatively weak disturbance at this point,
500 mb heights are expected to decrease on the order of 1-3 dam over
South-Central AZ, and so surface temperatures will cool by only a
few degrees tomorrow (highs ranging from 105-110 in the lower
deserts). As a result of the slight cooldown tomorrow, HeatRisk will
drop into the Moderate category. However, those planning outdoor
recreation during the weekend should continue to practice heat
safety measures, i.e., stay hydrated, seek shade or air conditioned
places, and take frequent breaks during physical activity.

High temperatures on Sunday and Monday drop to the low-to-mid
100s across the lower deserts, with ensemble mean 500 mb heights
generally ranging from 585-588 dam late this weekend into early
next week over the region. WPC cluster analysis continues to
depict good agreement between global ensembles with respect to the
upper level flow evolution. A shortwave trough approaches the
West Coast late Saturday into Sunday and becomes a closed low by
Monday. Ensembles still continue to show uncertainties in terms of
the overall position/strength of the closed low as it meanders
offshore near the latitude of the international border through the
middle of next week, which will dictate the positioning of
ridging downstream over the Southwestern US. Due to the proximity
of the closed low, high temperatures will likely be greater over
the South-Central AZ deserts than over Southeast CA. If a stronger
ridge does indeed develop over the area, another round of
excessive heat with highs of 110+ degrees will become more likely
in the Tuesday-Thursday timeframe.

&&

.AVIATION...Updated at 1740Z.

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

VFR conditions expected at all terminal for the forecast period. Winds
will continue to follow typical diurnal tendencies, with speeds
generally aob 10 kt outside of occasional gusts to around 15-20 kt
this afternoon and evening. Gusts to around 25 kts will be
possible at KIPL and KBLH later this afternoon through the
evening. SCT-BKN high clouds will continue throughout this
afternoon then skies will clear out overnight. Expect high SCT-
BKN clouds to return tomorrow for the South-Central Arizona
terminals.

&&

.FIRE WEATHER...
Hot and seasonably dry conditions will continue to support a high
fire danger across the area during the next several days.
Isolated thunderstorms developing over the White Mountains,
Mogollon Rim, and in the far eastern districts later today could
lead to an increased risk of lightning-related fire starts,
however, the chances of dry thunder across the far eastern
districts remains below 10 percent. Another day of excessive heat
is forecast across most of the lower deserts with highs near 110
degrees before a gradual cooldown over the weekend. Winds during
the next several days will continue to favor diurnal tendencies
with sustained speeds remaining below 15 mph along with occasional
afternoon breeziness upwards of 20-25 mph. MinRHs through next
week will hover at around 10% with poor to fair overnight
recoveries of around 20-40%.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST this evening for
     AZZ530>556-559>562.

CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ561-
     563-566-567-569-570.

&&

$$

DISCUSSION...Whittock
AVIATION...95/Smith
FIRE WEATHER...Lojero