643
FXUS65 KPSR 250511
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1011 PM MST Sun Nov 24 2024

.UPDATE...Updated 06Z Aviation Discussion.

&&

.SYNOPSIS...
Temperatures will remain above normal across the region through the
next week, with dry conditions prevailing and periods of mostly
cloudy skies. A weather system will pass the Desert Southwest to the
north during the middle of the upcoming workweek, but precipitation
chances should remain confined to northern Arizona.

&&

.DISCUSSION...
The region still finds itself between a broad area of negative H5
height anomalies over the Pacific Northwest centered offshore, and a
broad area of positive height anomalies centered over Baja
California and into Sonora. The resultant tightened pressure
gradient aloft has led to stronger zonal flow, with 500 mb RAP
analysis showing speeds between 50-65 kt over the forecast area.
This strong, zonal flow will continue to bring moisture-laden air
in the middle and upper levels inland, increasing cloud cover
over the course of the day that should persist through Monday.
Thanks to the increased cloud cover, highs today across the lower
deserts should be a few degrees cooler than what was observed
yesterday, mostly in the middle 70s, and overnight lows will be a
few degrees warmer. Similar highs are forecast Monday as well.

Quasi-zonal flow should persist over the region through much of the
upcoming workweek, though with slight variations in heights aloft,
the strength of the flow, and moisture aloft. Ensembles are in
excellent agreement that H5 heights will build during the latter
portion of the day on Monday into Tuesday, peaking around 582-585
dam over southern AZ. This will shift the stream of moisture further
north, temporarily clearing skies, and likely causing the warmest
afternoon highs of the next 7 days to occur on Tuesday, in the upper
70s to around 80F, followed by the warmest overnight lows Wednesday
morning. Latest NBM output shows widespread lower desert lows in the
50s Wednesday morning, with a 40-60% chance of temps staying at or
above 60F overnight in the typically warmer locales.

On Tuesday night, the return of thick cloud cover above the 500 mb
level will also be a factor in keeping overnight lows relatively
mild. Cloud cover will return as the Pacific Northwest low finally
moves onshore, suppressing heights aloft, once again tightening the
pressure gradient overhead, and thus drawing upper level moisture
back over the region. This weak shortwave will cause little in the
way of sensible weather impacts, though widespread breezy conditions
may develop behind a dry cold front that is expected to pass over
the area. Highs should drop a few degrees Wednesday, and flow aloft
will shift out of the northwest in the wake of the shortwave trough
as it passes north of the Desert Southwest.

Cluster analysis shows decent agreement between ensemble membership
even beyond midweek. All clusters depict a ridge over the
Northeastern Pacific, undercut by a closed low well offshore
centered approximately along 30 degrees north. Both features
approach the west coast late week. With continued quasi-zonal flow
during the latter half of the upcoming workweek, and an upstream
source for moisture aloft (the aforementioned closed low), GFS bufr
soundings indicate fairly persistent cloud cover. Latest NBM
deterministic output reflects this, as forecast temperatures stay
quite stable Thursday onward, with highs in the low to mid 70s and
lows in the upper 40s and 50s for the lower deserts. These forecast
temperatures are still around 5 degrees above average. Whether the
closed low can bring appreciable precipitation chances to
portions of the region next weekend is still a key forecast
uncertainty. As of now, PoP remain low next weekend, mostly below
20% across the forecast area.

&&

.AVIATION...Updated at 0511Z.

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

Winds will continue to follow their typical diurnal pattern with
speeds generally remaining aob 8 kt. Extended periods of light and
variable to calm winds can also be expected, especially during
wind shifts. High cirrus clouds will continue with a SCT layer of
clouds around 15-17 kft and a BKN-OVC cloud layer around 20-25
kft. Skies will start to clear tomorrow evening after 00Z, with
only FEW-SCT clouds with bases aoa 25 kft expected through the end
of the TAF period.

&&

.FIRE WEATHER...
Dry and warmer than normal conditions will persist across the
region for the next several days. Winds will follow generally
light and diurnal tendencies through Tuesday before some areas,
mainly across parts of the Arizona high terrain and Lower Colorado
River Valley, pick up some marginal breeziness Wednesday and
Thursday. Regional moisture content will be on the increase today
with MinRH values between 25-35% across the western districts.
Values across the eastern districts will only be 15-20% this
afternoon, but will increase to 20-25% by Monday afternoon. Fair
to good overnight recoveries can be expected through the middle
portion of the week.

&&

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

$$

DISCUSSION...Whittock
AVIATION...Berislavich
FIRE WEATHER...RW