National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KPSR 212050
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
150 PM MST Sun Apr 21 2024

.SYNOPSIS...
Unseasonably warm temperatures with mostly sunny skies will persist
through the first half of the week with the warmest days yielding
widespread minor heat-related health risks. The first in a series of
weather systems will move through the region Wednesday and Thursday
resulting in a temperatures retreating closer to the seasonal normal
while also supporting occasional periods of strong, gusty winds.

&&

.DISCUSSION...
Dry westerly flow under the influence of low amplitude ridging
remains situated over the SW Conus early this afternoon providing a
synoptic setup yielding much above normal temperatures. With H5
heights hovering near 580dm over the next 60 hours, temperatures 8F-
12F above normal should be common with tomorrow being the warmest
day. Very gradually through the middle of the week, anomalous
troughing over the East Pacific will edge towards the west coast
with modest height falls entering the western CWA as early as
Tuesday resulting in the first signs of a cooling trend. In
addition, the incoming system will force an increasingly tightened
pressure gradient and progressively prevalent afternoon gustiness
into the middle of the week.

Ensemble guidance is somewhat more consistent showing an initial
shortwave and compact vorticity center nearing the southern
California coast Wednesday with the bulk of the cold core lifting
through western and northern Arizona Thursday. As anticipated, the
timing of system is slightly slower than previously advertised such
that more robust midtropospheric height falls may wash across the
forecast area late Wednesday night/Thursday morning. This timing
would be somewhat unfavorable for momentum transfer of stronger pre-
frontal wind gusts into south-central Arizona Wednesday afternoon,
and then separated from the pressure gradient post-front on
Thursday. Nevertheless, periodic gusts 20-30 mph still looks
applicable Wednesday afternoon with stronger speeds preferred near
terrain features in the far western CWA.

After the initial wave ejects into the plains Thursday/Friday, the
flow pattern through the weekend (and perhaps into the beginning of
next week) will support mean longwave troughing over the western
Conus with a couple negative PV anomalies descending and
intensifying from the Pacific NW. The trajectory and depth of the
incoming energy suggests a continuation of dry weather for the
majority of the forecast area with only slight chances of very light
showers over higher terrain areas of Arizona. However, this
evolution will yield additional periods of stronger, gusty winds
ahead of the shortwave passage along with more pronounced cooling.
In fact, there is moderate to good forecast confidence readings will
fall to at least 3F-6F below normal over the weekend with NBM output
suggesting nearly a 40% chance Phoenix fails to reach 80F Saturday.

&&

.AVIATION...Updated at 1120Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected during the TAF period. Winds will
follow light and diurnal tendencies with periods of variability
between directional shifts. Other than a FEW passing high clouds and
mid-level cloudiness over the high terrain areas to the north and
east, skies will be mostly clear over terminal locations through
tonight.


Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during the TAF period. Winds will
be light and follow diurnal patterns. Other than a FEW passing high
clouds, skies should remain mostly clear through the forecast window.

&&

.FIRE WEATHER...
Dry conditions with above normal temperatures will persist early
this week with winds steadily becoming more breezy ahead of an
approaching weather system. Afternoon humidity levels will continue
to fall to around 10% following poor to fair overnight recovery of
20-40%. Cooler weather arriving during the latter half of the week
will allow an improvement to RH with afternoon values only falling
into a 15-25% range. As this weather disturbance moves through the
region later in the week, very breezy conditions will also
occasionally impact districts with afternoon gusts commonly reaching
20-30 mph. Given this combination of winds and humidity levels, a
periodic elevated fire danger should be planned for during the
second half of the week.

&&

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

&&

$$

DISCUSSION...18/Kuhlman
AVIATION...Young/RW
FIRE WEATHER...18