822
FXUS65 KPSR 231733
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1033 AM MST Sun Feb 23 2025

.UPDATE...Updated 18z Aviation Discussion...

&&

.SYNOPSIS...
Above normal temperatures will prevail through the next 7 days,
with a warming trend through midweek that will see high
temperatures climb into the upper eighties to near ninety by
midweek. Aside from periods of higher level clouds over the next
week, dry conditions will continue, and winds will be light most
days followed by some breezy conditions toward the end of the
week.

&&

.DISCUSSION...
Objective analysis and satellite imagery shortly after midnight
showed a rather weak, nearly indistinguishable, shortwave trough
passing through AZ, following the vapor trails of a better defined
shortwave moving east through the Southern Plains. The weak
shortwave is expected to push out of AZ by sunrise today. Mid-
level, 500mb, pressure heights will rise quickly behind this
shortwave, climbing up to 584-585dam by this afternoon. These
heights are more common for late-May/early-June. Despite this
rapid height increase the lower troposphere thermal profile will
be slower to respond, with 850mb temperatures only forecast to
rise 2-3C compared to yesterday afternoon. This will at least
translate to high temperatures this afternoon around 2-3F warmer
than yesterday, with lower desert highs forecast around 80-84
degrees. Sunny skies, light winds, and very dry conditions can be
expected again today.

Latest NBM forecast continues to show a daily warming trend
through midweek, with highs warming through the 80s, despite
greatest 500mb heights expected over the region today. The slower
lower level thermal response is expected to continue as ridging to
quasi-zonal flow persists through the early week. Over the last
24 hours, global models have made a slight shift toward not as hot
midweek, with lower probabilities for 90+ degree highs in the
lower deserts. There are a couple potential reasons for this
shift in models, plus this shift actually lines better from a
historical context. One reason could be the amplified ridge mid
to late week being more transitory and not as broad, which may
bring in influences of a Pacific low earlier. Another reason is
that there is a greater subset of global ensembles, as well as the
deterministic GFS and ECMWF, showing a shortwave trough dropping
south through AZ, on the eastern flank of the midweek ridge, in
the Thursday timeframe. From a historical perspective, hitting the
90 degree mark in February is very rare. It has only happened 7
times in Phoenix`s recorded history and only 1 time in the 2000s
(90F on Feb 17, 2016). Looking at that metrics of the one occasion
in 2016, 500mb heights were around 582-584dam and 850mb
temperatures were around 21-24C. Compare that to the current
midweek forecast of 576-580dam heights and 17-19C temperatures.
So, the latest NBM deterministic forecast with highs around 2-3
degrees lower than the forecast 24 hours ago seems more
reasonable. This forecast is still 4-5 days out and bound to
fluctuate a bit more, but will not take away from the fact that
temperatures will heat up this week with widespread Minor HeatRisk
expected. Some daily record high temperatures will be within reach
in Phoenix if it does reach 90+ degrees later this week, then
(see CLIMATE section below).

Besides the 80 to 90 degree heat this week, conditions are
expected to remain very dry, with afternoon minimum RH values as
low as 5-10%. Mostly sunny skies will prevail through most of the
week, with only thin high clouds at times. Winds are also expected
to be light most days, with some modest afternoon breezes (10-20
mph). The one exception will be late week, around Thursday, with
potential for breezy to windy conditions in South-Central AZ from
the shortwave trough dropping down from the north on the east
flank of the ridge. The ECMWF ensemble is most aggressive with
this shortwave and has Extreme Forecast Index values up to around
0.7-0.8 for wind and wind gust, which is indicative of an unusual
wind event for this time of year. This potential wind, combined
with the anomalous heat and very dry conditions could result in
elevated fire weather conditions.

By the end of the workweek and into next weekend, a pattern change
is expected, as the North Pacific Jet begins to retract and shift
equatorward. Upper level closed lows will begin to undercut the
ridge, bringing a more disturbed pattern to the Desert Southwest. An
initial closed low will be mostly dry, passing overhead possibly
Friday or Saturday, with timing differences apparent between WPC
Clusters. The main impacts from this initial systems will be locally
breezy conditions and the potential again for elevated fire
weather conditions for the high terrain of South-Central AZ.
Temperatures should begin to trend down as well, though latest NBM
shows them remaining above normal through at least Saturday. There
are already good indications that another, potentially more
impactful, Pacific trough will follow the first toward the
beginning of the following week.

&&

.AVIATION...Updated at 1735Z.

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

No aviation weather concerns are expected through at least Sunday
night under clear skies. Wind speeds will remain light with
directions following typical diurnal trends, but with some periods
of calm/variable winds at all terminals.

&&

.FIRE WEATHER...
The main concern for fire weather will be toward the latter half
of this week and into next weekend when a couple disturbances
bring potential for elevated winds speeds to go along with the
already very dry and anomalously hot conditions. The first
disturbance looks to impact the region in the Thursday timeframe
and the second in the Friday-Saturday timeframe. Increased fire
weather concerns look to mostly be in the AZ deserts with both
disturbances. Through this entire week afternoon temperatures will
be running upwards of 10-15 degrees above normal, with highs
reaching the upper-80s to 90F by midweek. Daily MinRHs of 5-15%
will persist with fair to poor overnight recoveries to around
25-30%.

&&

.CLIMATE...

Record high temperatures next week:

Date         Phoenix           Yuma         El Centro
----         -------           ----         ---------
Feb 24      91 in 1904      93 in 1986      92 in 1986
Feb 25      92 in 1921      95 in 1986      94 in 1986
Feb 26      91 in 1986      96 in 1986      95 in 1986
Feb 27      92 in 1986      95 in 1986      96 in 1986
Feb 28      89 in 1986      97 in 1986      92 in 1986

&&

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

$$

DISCUSSION...Benedict/Whittock
AVIATION...Young/Kuhlman
FIRE WEATHER...Benedict/Kuhlman
CLIMATE...18