122
FXUS65 KPSR 262318
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
415 PM MST Wed Jun 26 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
A period of drying conditions will carry through the end of the week
with rain chances decreasing to near zero across south-central
Arizona by Friday. Moisture and subsequent rain chances begin to
increase into next week. Above normal temperatures will persist
through at least early next week with lower desert highs approaching
or exceeding 110 degrees each day, especially in some of the
typically hotter locales.

&&

.DISCUSSION...
Current mid-level wv imagery reveals the center of a subtropical
high pressure system approximately over southern New Mexico near the
international border, with abundant moisture in place over the four
corners region and extending south. RAP analysis shows PWATs over
the region ranging from 1.4-1.9" as of late this morning, but these
values will be on the decline today through late Friday/early
Saturday, as a strong trough currently off the Pacific Northwest
Coast begins to push onshore, enhances southwesterly flow, and
brings drier air aloft over the Desert Southwest.

With abundant moisture in place over much of Arizona and the
remnants of an MCV near Flagstaff, convective activity was already
ramping up late this morning over the Mogollon Rim/Central AZ high
terrain and is expected to continue through much of the afternoon.
As South-Central AZ is in the wake of this MCV, subsidence aloft
should provide a sufficient cap to thunderstorm development over the
lower deserts late this afternoon/this evening (less than 10% chance
for measurable rainfall over the lower deserts), but chances for
thunderstorms over the high terrain to the north/east of Phoenix
remain around 10-20%. The primary hazards associated with any
thunderstorms today will be lightning, locally heavy rainfall, and
gusty outflow winds (HREF indicates a 10% probability for gusts in
excess of 35 mph for portions of northern and far eastern Maricopa
County). Forecast highs for this afternoon range mostly from 107-112
degrees across the lower deserts.

As mentioned previously, the trough off the Pacific Northwest Coast
will have a significant influence on moisture over the Desert
Southwest through early this weekend as it moves onshore and passes
to the north early Friday. Enhanced southwesterly flow will act to
scour out mid level moisture and eventually some low level moisture,
leading to ensemble mean PWATs dropping as low as 0.9-1.3" across
Southern AZ. As drier air settles in from west to east over the next
several days, chances for rain decrease as well. Rain chances will
essentially come to an end starting Thursday with only slight
chances remaining over far eastern and northern Arizona. Friday is
still expected to be our driest day. By Saturday, ridging will begin
to build back over the region from the east, with southeasterly flow
re-establishing over the southeastern corner of the state. GEFS/ENS
model soundings depict weak southerly/southeasterly flow by Sunday
over South-Central AZ, with moisture beginning to creep back into
the region and rain chances increasing within our eastern CWA.
Ensemble mean PWATs increase back up to the 1.5-1.75" range by
Monday, and this moisture is expected to linger through the middle
of next week, leading to daily chances for isolated to scattered
thunderstorms mostly over the high terrain (30-50%) and potentially
making it into the South-Central AZ lower deserts (10-30%).

Forecast temperatures for the rest of the week and even through
early next week vary only a few degrees day to day. Above normal
temperatures of 3-5 degrees are expected nearly every day with lower
desert highs mostly topping out between 106-112 degrees each day.
Despite these readings falling into a Moderate HeatRisk category,
the heat will still be dangerous to those most vulnerable and to
those that underestimate the heat. The hottest day is likely to fall
on Sunday as the sub-tropical high strengthens over the weekend,
despite it already shifting eastward away from the region. Forecast
highs Sunday are currently between 107-113 degrees across the South-
Central Arizona lower deserts to 108-115 degrees across the western
deserts. The latest NBM forecast temperatures Sunday do present some
localized areas of Major HeatRisk, so Excessive Heat headlines may
eventually be needed for small portions of the area. Going through
the first half of next week, the increased moisture and monsoon
activity along with lowering heights aloft should allow for
temperatures to attempt to cool off closer to normal readings.

&&

.AVIATION...Updated at 2315Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues should affect the Phoenix terminals through
Thursday afternoon under mostly clear skies as reduced thunderstorm
activity in the region significantly reduces the chances for aviation
impacts. Probabilities for outflow winds descending south into the
metro are still only around 10% with chances greatest at KSDL/KDVT,
while storm chances are under 5%. West winds should prevail well
into the overnight with the typical switch to easterly only probable
at KIWA. In fact, winds at KPHX may only become light and variable
for a few hours after sunrise before reverting back to westerly.


Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Thursday afternoon under only
a FEW occasional mid/high clouds. Winds should vary between SE and
SW through the period with afternoon/early evening gusts 20-25kt
common at KBLH.

&&

.FIRE WEATHER...
The weather pattern through the rest of the week will allow for
drying conditions and much lower chances for rain. Isolated
thunderstorm chances today are expected to be limited to the higher
terrain north and east of Phoenix before chances basically come to
an end starting Thursday. MinRHs will lower back into the teens
across the lower deserts by Thursday, while overnight recoveries
remain good at 35-50%. Winds will be fairly light today with some
periodic afternoon breeziness, before increasing more on Thursday
with afternoon gusts commonly reaching 20 mph. Gusts Thursday
evening for portions of western Imperial County and JTNP could reach
upwards of 30 mph and locally up to 40 mph for several hours. The
dry conditions with virtually no chances for rain should persist
through Saturday before moisture returns Sunday, increasing
humidities and potentially bringing back chances for thunderstorms
across south- central and eastern Arizona. Temperatures through the
period are expected to average several degrees above normal.

&&

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

&&

$$

DISCUSSION...Whittock
AVIATION...18
FIRE WEATHER...Whittock/Kuhlman