642 
FXUS65 KPSR 272322
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
422 PM MST Tue May 27 2025

.UPDATE...Updated 00z Aviation Discussion...

&&

.KEY MESSAGES...

-Seasonably hot and dry through Thursday, with highs in the upper
 90s to lower 100s.

-A pattern shift late this week will result in a slight boost in
 temperatures, with highs peaking around 99-107 across the lower
 deserts on Friday leading to areas of Moderate HeatRisk.

-An influx of tropical moisture over the weekend may cool 
 temperatures to near normal by Sunday and lead to slight chances 
 for showers (20-40%) and isolated thunderstorms for portions of 
 Southwest and South Central Arizona.

&&

.DISCUSSION...
The latest objective analysis data shows weak troughing meandering 
over the Desert Southwest, while upper level ridging continues to 
build over much of the western CONUS with positive height anomalies 
extending into western Canada. Temperatures continue to run close to 
seasonal normals as a result with lower desert highs forecast to top 
out in the 97-103 degree range for most lower desert locales through 
Thursday. Dry conditions will continue across our area over through 
the end of the workweek with light winds and some afternoon breezes 
expected each day. 

Getting into the end of the workweek, a shortwave that is currently 
about 800 miles off the California coast over the eastern Pacific 
will continue to propagate eastward before cutting off near the 
northern Baja Peninsula. As this occurs, upper level ridging will 
again build across much of the western CONUS leading to increasing 
positive height anomalies over our area. Operational and ensemble 
guidance show 500 mb heights rising to around 586-589 dm over the 
forecast area, which is about the 90th climatological percentile. 
Forecast highs top out Friday in the 99-107 degree range for most 
lower elevation areas and 97-102 degrees for some of our higher 
elevation communities such as Globe and San Carlos. As a result, we 
will see more widespread coverage of Moderate HeatRisk Friday, so 
folks and those particularly sensitive to the heat should exercise
the necessary heat safety precautions to avoid any heat related 
illnesses.

In addition to the aforementioned cutoff low, a tropical system 
currently south of the southern Mexico coast will continue to 
advance northward off the coast of western Mexico. The latest NHC 
update now shows a 100% chance of tropical depression or tropical 
storm developing from this area of interest tonight or tomorrow. 
While we aren't expecting this tropical system to move into our 
area, ensemble and deterministic guidance continue to show tropical 
moisture getting transported northward into the southwest CONUS 
thanks to the cutoff low. Global ensembles have trended up on 
moisture and now have PWATs closer to 1.2-1.3" with the latest EPS 
now showing most of its members showing values around 1.3-1.4". 
Given that this time of year is typically very dry, PWAT anomalies 
as result climb in excess of 200-250% of normal. This moisture 
combined with forcing from the low will support increasing rain 
chances for the upcoming weekend. Guidance continue to come into 
better agreement in the evolution of this cutoff low, though there 
are still discrepancies in the exact timing and track of the low as 
it moves inland. As of now, ensemble and deterministic guidance 
support the low moving inland Sunday into early Monday. Forecast 
soundings show increasing instability Sunday afternoon and will 
support increasing thunderstorm chances across the region. Gusty 
winds and locally heavier rainfall totals may accompany any 
thunderstorm development that we see. Exact QPF remains uncertain,
but for now the latest WPC amounts support Arizona lower desert 
areas seeing generally less than 0.10" with higher amounts across 
the high terrain north and east of Phoenix. Stay tuned as we 
continue to fine-tune the forecast.

&&

.AVIATION...Updated at 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT:
No aviation weather concerns will exist during the TAF period. The
overall wind pattern will continue to exhibit the typical diurnal
tendencies with speeds aob 10 kts, although some occasional gusts
into the mid to upper teens will be possible through early this
evening and once again for Wednesday afternoon/early evening.
There will also likely be some periods of light and variable
winds, especially during diurnal transitions. The SCT to BKN high
clouds currently overhead will gradually clear out heading into 
the evening and overnight hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected through Wednesday afternoon
under generally mostly clear skies with some passing high clouds.
At KIPL, current SE winds will shift out of the SW for a period
this evening before shifting back out of the SE during the
overnight hours. At KBLH, winds will generally fluctuate between
the S-SSW. The overall wind speeds at both terminals will remain
aob 10 kts. 

&&

.FIRE WEATHER...
Very dry conditions will continue through the next couple of days
as Min RHs range between 5-15%. Overnight Max RHs will generally
range between 20-40% with locally higher values across Imperial
County. Winds will favor typical diurnal tendencies with afternoon
gusts to around 15-20 mph. Temperatures will be near to slightly
above normal over the next couple of days before peaking on
Friday. An unsettled weather pattern then takes shape for this
upcoming weekend and will lead to cooler temperatures and
increasing chances for showers and thunderstorms.

&&

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

$$

DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Smith