Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 260954
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
254 AM MST Tue Mar 26 2024

.SYNOPSIS...
A weather system lingering across the region will continue to
bring chances for showers and a few isolated thunderstorms today
from Phoenix into the higher terrain north and east of Phoenix.
High pressure will then settle over the region starting Wednesday
bringing in drier conditions and a strong warming trend. High
temperatures are forecast to top out in the lower to middle
eighties by Thursday. A stronger weather system is then expected
to bring a period of unsettled weather with increased rain chances
and cooler temperatures from Sunday into early next week.

&&

.DISCUSSION...
Broad troughing from the Plains States through much of the Western
U.S. continues to bring unsettled weather to portions of the
Desert Southwest. Despite drier conditions that worked into the
much of the area Sunday night into early Monday, scattered
showers and even a few thunderstorms have been seen across south-
central and eastern Arizona since Monday afternoon. Colder air
aloft under the broad troughing continues to provide steep lapse
rates and some minimal instability for this activity to develop.
A weak PV anomaly barely discernible within water vapor imagery
is also helping to maintain early morning showers currently moving
across the area. These early morning showers are likely to
diminish by or just after sunrise as the PV anomaly moves to the
east, but another piece of energy is then likely to traverse
across central Arizona by this afternoon. Hi-res CAMs are
generally only showing redevelopment this afternoon across higher
terrain areas north and east of Phoenix, but given similar lapse
rates as yesterday as well as even a bit more moisture, conditions
may allow for some convection impacting the Phoenix area this
afternoon/early evening. Overall impacts are expected to be very
minimal with rainfall amounts generally less than a tenth of an
inch over the majority of the area and at most some small hail
with any weak thunderstorms that develop.

Starting Wednesday, the trough will finally exit east of the
Phoenix allowing for increasing subsidence aloft as a weak ridge
moves in from the west. Drier and warmer air will filter into the
region during the latter half of this week with lower desert high
temperatures topping out in the lower to middle 80s starting
Thursday and likely lasting into Saturday. These tranquil weather
conditions are then expected to abruptly come to an end on Sunday
as a rather potent low pressure system moves into the region from
the west.

Ensemble guidance now seems to be in better agreement with the
evolution of the low pressure system for late weekend into early
next week. The trough is first shown reaching the Pacific
Northwest Wednesday into Thursday before tracking southward just
off the California coast Friday into Saturday. Further
strengthening of the upper level trough is likely to occur as it
tracks southward off the coast of California with 500mg heights as
low as 536-540dm off the southern California coast on Saturday.
This would represent near climatological MIN 500mb heights for the
period, while the upper level jet over the Desert Southwest late
Saturday into Sunday reaches into the 99th percentile with speeds
of 120-140 kts. Nearly all signs are pointing toward a rather
strong weather system eventually moving through our region on
Sunday into Monday, but it will be in a weakening phase by then
and there is still some uncertainty how much it will weaken before
it moves through the area. As of now there are likely at least
two periods of potentially impactful weather with an initial
period of near advisory level southwesterly winds before FROPA
followed by a likely strong frontal band with moderate rainfall
and possibly some embedded thunderstorms traversing the area at
some point on Sunday. Thereafter for a day or two into early next
week, much of Arizona is likely to fall under a cold core scenario
with daytime showers and isolated thunderstorms possible. The
latest QPF for the entire event generally shows 0.25" across the
western deserts to 0.50-0.75" across the south-central Arizona
lower deserts. QPF over the higher terrain of central Arizona
could possibly see as much as an inch or more during the event.

&&

.AVIATION...Updated at 0612Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Showers have cleared the metro area at this time. However,
additional isolated showers may develop near or in the metro
tonight through about sunrise Tuesday. Most rain will focus just
east of Phoenix. Any shower will be capable of producing brief
strong gusty winds. Wind speeds between 0.5-3K ft AGL will
increase to as high as 35-40 kts between now and 09Z. This is not
expected to fully translate to the surface, but could lead to
brief wind gusts in excess of 20 kts. Minor LLWS may also be
generated as a result. Winds then subside and shift E at all
terminals by 10-11Z. Similar conditions to Monday are expected
Tuesday, with afternoon SW`rly gustiness and convective showers
and storms developing and passing mainly off to the NE and E of
the metro in the afternoon. The convection tomorrow afternoon will
be capable of pushing outflows southward into the Phoenix metro in
the evening. Cloud coverage will remain primarily FEW to SCT, with
cloud bases mainly around 8-10K ft. However, cumulus may develop
as low as 5K ft Tuesday morning before rising.

Southeast California/Southwest Arizona including KIPL and KBLH:
Gusty W-SW winds will continue at KIPL for the next few hours
before subsiding. Elevated W winds will continue at KIPL through
Tuesday afternoon, with gusts during the afternoon and evening up
to 20-25 kts. Winds will be lighter at KBLH, with sustained speeds
up to 10 kts during the day and gusts to around 20 kts in the
afternoon. W to SW directions will prevail at KBLH. FEW to SCT
high clouds will pass over the area through tonight. FEW CU may
develop again Tuesday afternoon near KBLH. Otherwise, skies will
be mostly clear.

&&

.FIRE WEATHER...
Today will bring additional chances for mainly higher terrain
light showers and a few isolated afternoon thunderstorms before
high pressure settles over the region starting Wednesday. Winds
today will be breezy at times, particularly in the afternoon,
with gusts of 20-25 mph before diminishing into Wednesday. MinRHs
today will range from 15-20% over the western districts to 25-30%
over the lower deserts of south-central Arizona, and up to 50%
over the Arizona high terrain. Drier and warmer conditions
starting Wednesday will lower MinRHs across all of the lower
deserts into the teens to around 20% with day to day afternoon
breeziness persisting. Slightly above normal temperatures and dry
conditions are then expected to last into the early part of the
weekend before unsettled weather conditions move in by Sunday.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Benedict
FIRE WEATHER...Kuhlman


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