504
FXUS65 KPSR 221711
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1011 AM MST Tue Apr 22 2025

.UPDATE...Updated 18z Aviation Discussion.

&&

.SYNOPSIS...
Dry and seasonably warm conditions will persist through the end of
the workweek. A dry weather system is expected to enter the Desert
Southwest this weekend, bringing breezy to locally windy conditions
and cooling temperatures to slightly below seasonal normals for a
few days.

&&

.DISCUSSION...
Quasi-zonal flow is expected to remain in place over the Southwest
US through much of the rest of the workweek, resulting in little day-
to-day sensible weather changes through at least Thursday. Expect
afternoon highs to range mostly from the upper 80s to lower 90s
across the lower deserts, which is near to only slightly (up to 5F)
above normal for the time of year. Global guidance suggests a weak
weather disturbance moving through the Western US late Wednesday,
which could help develop/enhance gusty Sundowner winds in the
typically prone areas of Western Imperial County Wednesday evening.
Otherwise, the main focus of the forecast period will be the
potential for elevated fire weather conditions from the approach
of a more potent upper level low late week into this weekend.

Ensembles depict the center of an area of negative H5 height
anomalies just off the West Coast early Friday gradually moving
onshore and over the Great Basin this weekend. While WPC Clusters
suggest considerable uncertainty in strength and exact position of
this upper low Friday onward, all the potential outcomes shown in
the clusters would result in very similar impacts, with
essentially zero chances for precipitation. The impacts would be
increased winds across the forecast area as early as Friday,
especially during the afternoon and early evening, as well as a
cooldown areawide to the lower to middle 80s as early as Saturday.
The increased winds and continued dry, warm conditions (though
slightly cooler than during the workweek) would lead to locally
elevated fire weather conditions, particularly for the high
terrain east of Phoenix.

Depictions of the upper level flow over the Western US diverge
significantly between ensemble members heading into the middle of
next week, though the upper low is likely to weaken and pass east of
the area early next week. This allows H5 heights to slowly rebound
to near average for the time of year, and temperatures at the
surface would warm back to seasonal levels in response.

&&

.AVIATION...Updated at 1710Z.

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

No aviation weather concerns under clear skies can be expected
throughout the TAF period. The overall wind pattern will continue
to exhibit the typical diurnal tendencies with overall speeds aob
10 kts. There will likely be periods of light variability to even
calm conditions, especially during the diurnal transition.

&&

.FIRE WEATHER...
Dry and tranquil weather conditions will persist through much of
the remainder of the workweek, with slightly above normal
temperatures. MinRH values each day will bottom out near 10%
areawide with poor to fair overnight recoveries. Fairly light and
diurnally driven winds are expected through at least Thursday,
with some afternoon upslope breeziness. Winds are likely to
increase by the end of the week into this weekend as an upper
level low pressure system moves into the western United States.
This may lead to locally elevated fire weather conditions,
particularly for the high terrain east of Phoenix during the
weekend, though temperatures will cool to slightly below normal.

&&

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

$$


DISCUSSION...Whittock
AVIATION...Lojero
FIRE WEATHER...Whittock