962
FXUS65 KPSR 040019
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
519 PM MST Thu Apr 3 2025

.UPDATE...
Updated Aviation discussion.

&&

.SYNOPSIS...
A broad trough of low pressure continues to remain entrenched over
the Desert Southwest. This troughing feature will keep temperatures
well below normal and bring chances for light precipitation to
mainly the higher terrain areas of southcentral AZ through
Saturday. From late this weekend into the middle of next week, a
significant warming trend will transpire with highs climbing into
the upper 90s to around 100 degrees across the lower deserts.

&&

.DISCUSSION...
A broad and anomalously deep trough continues to remain the
predominant feature over the western CONUS. This trough has been
responsible for keeping temperatures well below normal over the past
couple days and has brought some light shower activity to our region.
Isolated to widely scattered showers have developed again this
afternoon, however the boundary layer is much drier than yesterday
with dew points currently sitting in the upper 20s and lower 30s.
Therefore, most of this shower activity is falling as sprinkles or
virga. There will still be a low chance (10-30%) for accumulating
precipitation in the foothills and high terrain NE of Phoenix
through this evening. Winds have been noticeably calmer this
afternoon due to the southward shift of the mid-lvl jet. Most
locations should see speeds remaining at or below 10 mph with the
exception of SE California where gust will pick up to around 20-25
mph after sunset. Lows will again be on the cool side tonight,
ranging from the lower 40s to around 50 degrees across the lower
deserts.

On Friday, the upper-lvl trough will continue to deepen over the
Desert Southwest with 500 mb hghts becoming closed off over
southcentral AZ. The cold core aloft should pass near or directly
over the Phoenix Metro by the afternoon, resulting in increased lift.
Scattered showers are expected to develop around the periphery of
the low pressure circulation with much of the activity expected to
again remain confined to the higher terrain areas NE of Phoenix as
well as the mountains in E Pinal and W Maricopa Counties where PoPs
are around 20-30%. Due to the better instability and steeper lapse
rates associated with the cold core aloft, a few lightning strikes
and/or small hail will be possible with any shower that develops.
Temperatures on Friday will again be around 10-12 degrees below
seasonal norms with highs topping out in the low to mid 70s across
southcentral AZ and mid to upper 70s in southwest AZ and southeast
CA. Aside from a few lingering showers across the eastern Arizona
higher terrain on Saturday, the rest of the area will remain dry
with highs warming into the upper 70s to low 80s. As the low
pressure system pulls away from the region, an increased mid-lvl jet
on the back side of this system will result in stronger winds across
southeast CA and the Lower Colorado River valley Saturday afternoon
where gusts could reach 25-35 mph.

&&

.PREVIOUS DISCUSSION...
The weather pattern starting Sunday will then shift keeping any
weather systems over the northern Pacific into western Canada
allowing an upper level ridge to gradually build over the
Southwestern U.S. Forecast H5 heights are seen reaching near 580dm
by late Monday, to around 584-586dm on Wednesday, before potentially
peaking near 588dm next Thursday. Ensemble guidance shows this
upper level ridge likely reaching near climatological record
strength for next Wednesday-Friday, potentially pushing high
temperatures to around or just above 100 degrees across the lower
deserts late next week. Temperatures are forecast to warm about 5
degrees per day from Saturday through Thursday with highs topping
90 degrees by Tuesday and well into the mid to upper 90s by next
Thursday. Areas of Moderate HeatRisk are likely to develop during
the latter half of next week, with the hottest temperatures likely
focused from Thursday-Saturday. There is still some model
uncertainty with the eventual strength of the ridge and how hot it
will get, but we are nearly assured of seeing highs reaching 100
degrees for at least some of the lower desert late next week.

&&

.AVIATION...Updated at 0020Z.

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

Earlier shower activity over/near the Greater Phoenix area was
very weak. But, with evaporative cooling, downburst-like winds
were occurring with the main one originating over western Pinal
County which sent southerly gusty winds over KPHX and KIWA. That
activity has pretty much dissipated although there are satellite
indications of a similar swath of winds moving northwestward over
southern Maricopa County and western Pinal County. Would
anticipate that to dissipate before affecting any Phoenix area
TAFs but bears watching. Another area that bears watching is
Yavapai County which has ongoing light shower activity. The hi-
res models have various depictions of N/NWly winds overspreading
the TAFS this evening (though not as strong as this afternoon`s
gustiness) likely associated with precipitation cooled air. In the
meantime, light winds favoring S/SWly directions can be expected.
After the N/NWly winds this evening (if they materialize),
anticipate light and variable winds.

During the day Friday, westerly winds develop between 16Z-18Z.
Another round of weak shower activity is expected during the
afternoon. This time, showers are more apt to move roughly from
north to south leading to gusty N/NWly winds developing between
22Z-00Z.


Southeast California/Southwest Arizona including KIPL and KBLH:

Anticipate familiar diurnal wind patterns tonight before N/NWly
winds develop between 17Z-19Z. Expect gusts of 20-25kts at KBLH
(less so at KIPL). As for sky cover, isolated weak showers by pass
by the vicinity of KBLH before 03Z but not enough confidence to
include VCSH in the TAF (showers remain well away from KIPL).
Pockets of ceilings around FL100 will decrease after sunset.
Anticipate very little cloudiness during the day Friday.


&&

.FIRE WEATHER...
Well below normal temperatures and isolated to widely scattered
showers will be possible through Friday. There is also a low
chance (10-15%) for an isolated thunderstorm Friday afternoon and
evening, mainly over the foothills and high terrain of southcentral
AZ. Due to the isolated nature of the shower activity, the chances
for wetting rainfall will remain low at less than 10%. A warming
and drying trend will transpire through this weekend as MinRHs
lower from 15-25% areawide Friday to around 10-15% over the
weekend. Winds are expected to increase out of the northwest
Friday and Saturday with afternoon gusts ranging from 20-30 mph,
locally higher across the western districts. High pressure will
eventually settle back into the region by Sunday into early next
week resulting in a rapid warming trend and seasonably dry
conditions.

&&

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

$$

DISCUSSION...Salerno
PREVIOUS DISCUSSION...Kuhlman
AVIATION...AJ
FIRE WEATHER...Salerno