345
FXUS65 KPSR 251152
AFDPSR

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

.UPDATE...
12Z Aviation Discussion.

&&

.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 1150Z.

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

A southeasterly wind shift has transpired across the Phoenix
Metro area. This shift is only expected to be temporary as winds
will then switch back to westerly by 16Z. Speeds will increase up
to 10-15 kts with gusts in the 20-25 kt range this afternoon and
early evening before quickly diminishing by sunset. Winds should
remain aob 7 kts overnight, returning to the east around 08Z-09Z.
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 forecast period. There is currently a lull in gusts
this morning, however winds will ramp up again by this afternoon
at both terminals. Gusts around 25-30 kts will be common at KIPL
and up to 25 kts at KBLH. Gusts may linger past sunset at KIPL,
but winds will gradually diminish overnight. 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...Salerno
FIRE WEATHER...Whittock