521
FXUS65 KPSR 251047
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
347 AM MST Sat May 25 2024

.SYNOPSIS...
Widespread breezy conditions and below normal high temperatures can
be anticipated this afternoon as a weak area of low pressure moves
over the region. Daily highs are forecast to increase starting
tomorrow, with a ridge of high pressure building over the Desert
Southwest early next week. Triple digit highs return across much of
the lower deserts by Memorial Day and are expected to persist
through the middle of next week.

&&

.DISCUSSION...
The axis of a shortwave trough is moving onshore along the Southern
California Coast early this morning. West southwest winds aloft have
increased ahead of this trough (currently 30-35 kt down to ~650 mb
as observed in ACARS soundings at Sky Harbor) and are expected to
peak this morning before daytime heating can mix down this higher
momentum air to the surface. As such, winds will increase earlier in
the day today than they did yesterday, and peak gust values around
20-25 mph are forecast over much of the lower deserts this
afternoon. Peak gusts may be closer to 25-35 mph across portions of
Imperial County late this afternoon and early this evening. The
South-Central AZ high terrain east of Phoenix will be more breezy
than the lower deserts, with HREF probabilities of 30+ mph gusts
ranging between 10-40%. HREF probabilities for gusts to 35+ mph
drops off significantly to near zero in these locations, though some
isolated gusts to 35 mph are possible. As a result, locally elevated
fire weather conditions will exist along the South-Central AZ high
terrain east of Phoenix this afternoon.

Aside from widespread breeziness, the trough passing over the region
today will bring cooler temperatures. Highs this afternoon will
range from the upper 80s to lower 90s across the lower deserts -
values which fall between 5-10 degrees below normal for the date.
These below normal temperatures will be short lived.

In the wake of the trough, temperatures are expected to rebound to
near normal Sunday and continue increasing through the middle of
next week as a ridge of high pressure builds over the western CONUS.
Triple digit highs are likely (>70% chance) in Phoenix by Memorial
day, with Tuesday shaping up to be the hottest day this week.
Locally moderate HeatRisk will accompany the higher temperatures
this upcoming week - as early as Monday in Southeastern California
and Tuesday in the Phoenix Metro Area.

Though global ensembles are in excellent agreement on the ridging
pattern over the western CONUS through the middle of next week,
solutions begin to diverge late next week. By the Thursday-Friday
timeframe, disagreement exists over the evolution of a troughing
feature over the Pacific Northwest. Recent GFS model runs show a
trough moving onshore late Wednesday into Thursday, remaining far to
the north and potentially sending some transient disturbances over
the Desert Southwest along its base by Friday. This solution would
be consistent with the deterministic NBM temperatures decreasing to
near or slightly above 100 degrees late next week. The uncertainty
in the upper air pattern late next week is reflected in the NBM
temperature spread, with inner quartile values ranging from 100-105
degrees for Phoenix on Thursday and Friday. Dry conditions with near-
zero rain chances can be expected with more certainty through the
end of the month.

&&

.AVIATION...Updated at 0550Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Westerly winds around 10 kt will continue into the overnight hours
before switching to easterly around 10-11Z with speeds aob 8 kt.
Winds will then switch back westerly during the mid-to-late
morning hours. Westerly winds will then gust 15-20 kt during the
afternoon and early evening hours before decoupling after sunset
with speeds lessening to aob 7 kt for the evening and overnight hours.
Clear skies will continue through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds will remain westerly at KIPL and southwesterly at KBLH
through the TAF period. Wind speeds have started to come down at
both sites. At KIPL winds will gust to around 25 kt through the
overnight hours before picking back up with gusts of 25-30 kt for
the afternoon and evening hours tomorrow. At KBLH winds will gust
around 25 kt over the next couple of hours before lessening to
speeds around 10 kt for the overnight and morning hours tomorrow.
Winds will then gust 15-20 kt during the afternoon and evening
hours tomorrow. Clear skies will continue through the TAF period.

&&

.FIRE WEATHER...
Locally elevated fire weather conditions will exist today,
particularly over the high terrain of the eastern districts, as a
weak system helps to generate widespread breezy conditions. Gusts
over the high terrain of the eastern districts will peak between
25-30 mph, with isolated gusts potentially up to 35 mph. Gusts
will peak mostly between 20-25 mph this afternoon elsewhere across
the lower deserts. MinRH values will range between 10-20% today
and locally higher in the high terrain, and will drop to 10-15%
tomorrow. Overnight recoveries will be fair tonight at around 30-
50% and drop to 25-40% Sunday night. Hot and dry conditions will
persist after today, with generally lighter wind speeds and
typical afternoon breeziness each day. Daily highs will reach the
century mark in many lower desert locations by Monday and values
generally top out between 100-105 through the middle of next week.


&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 9 AM PDT this morning for CAZ562.

&&

$$

DISCUSSION...Whittock
AVIATION...Berislavich
FIRE WEATHER...Whittock