991
FXUS63 KDMX 240404
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1104 PM CDT Mon Sep 23 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Chances for light rain/showers southeast tonight and far west
  late tonight into Tue morning.

- Localized fog may occur tonight.

- Next rain chances arrive late this week and into the weekend.

&&

.DISCUSSION...
Issued at 250 PM CDT Mon Sep 23 2024

Weak ridge of high pressure is over Iowa this afternoon but despite
the high pressure, some moisture has been moving into southeast and
even parts of central Iowa. The combination of a slow moving upper
level PV anomaly directly over central Iowa and an initial wave of
theta-e advection into central Iowa has resulted in some elevated
light showers to develop between Ames and Waterloo. There is a very
dry layer below these showers so a fair amount of evaporation is
occurring yet a brief period of sprinkles or very light rain may
reach the surface. The PV anomaly will continue to move slowly off
to the northeast into this evening. A more robust upper level PV
anomaly/short wave is moving into the western Dakotas this afternoon
with good darkening showing up on the latest water vapor imagery.
This system will descend swiftly southeast tonight and will arrive
over northwest Iowa late. This system will bring a few showers to
western and perhaps north central Iowa late tonight into Tue morning
though any rain accumulations will be minor. Additional shower
chances will be over far southeast Iowa as more theta-e advection
rotates through that area tonight. There may be a few pockets of fog
to form overnight and it is possible it could be locally dense in
clearing areas near fringes of cloud cover.

Rain chances will be low on Tuesday outside any residual showers
lingering in the morning. The northern system will drag the thermal
trough over Iowa on Tuesday. That system may keep an abundance of
cloud cover around as well during the day, pending some clearing at
some point in the afternoon. High temperatures on Tuesday are
currently forecast in the upper 60s to low 70s but that is probably
on the optimistic side and should clouds prevail, these highs may be
3-5 degrees too high. The northern short wave will evolve into a
large closed upper low pressure system over the lower Mississippi
River Valley by Wednesday and will remain there into the early
portion of the weekend, effectively clogging up the upper level
flow. The area will be mostly quiet into Friday before some Gulf
moisture takes a non-typical route towards Iowa from the Florida
panhandle and wrap northwest around the upper low. That moisture may
be additional fueled if the currently Potential Tropical Cyclone
Nine is ingested into this flow. At some point, rain chances will be
on the increase this weekend as some short wave energy is ingested
into the flow as well. Overall this is a low confidence period due
to all of the moving parts but the potential for rain across at
least southeast Iowa, is increasing. Temperatures will generally be
in the 70s throughout with overnight lows in the 40s and 50s.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1104 PM CDT Mon Sep 23 2024

Expectations haven`t changed much since 00z. Conditions
approaching 06z vary from mostly clear/VFR northwest to
overcast VFR/MVFR conditions southeast with spotty IFR already
in place as well. Confidence in how these trends evolve is low,
but generally conditions should worsen along the northwestern
edge of the current VFR/MVFR ceilings during the overnight hours
with fog and/or stratus development. Current expectations are
for MVFR/IFR at KDSM/KOTM/KMCW, but lower LIFR conditions are
possible, with restrictions at other sites possible as well.
Confidence increases that VFR conditions will return later in
the morning and through the day with varied ceilings and cloud
heights.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Donavon
AVIATION...Small