572
FXUS63 KDMX 011136
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
636 AM CDT Sat Nov 1 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Sporadic light rain/drizzle chances through the afternoon then
  diminishing into the evening.

- Cool temperatures overnight. Potential for fog/freezing fog in
  the eastern half of the area early Sunday morning.

- Breezy and warmer on Sunday.

&&

.UPDATE...
Issued at 318 AM CDT Sat Nov 1 2025

Light radar returns can be seen over northern and north central Iowa
early this morning, as the upper low and coincident forcing squeaks
what little moisture it can out of the atmosphere. Precipitation
observations have been sporadic at best, teetering between light
falling rain and a drizzle/mist. Fortunately, with cloud cover
overhead, temperatures remain above freezing in the mid to upper
30s. This patchy light rain/drizzle will continue drifting
south and eastward through the morning and into mid-day today.

By this afternoon, much of the area will be on the backside of the
wave but weak instability will still be present over the
eastern half of the area. Soundings would indicate the boundary
layer will be too dry for rain to fall through, especially with
the surface high nudging in from the west. However, with the
stratus limiting mixing and forcing still present, have
maintained scattered light rain chances (15 to 20%) through
this afternoon before diminishing in the evening.

Tonight, surface high pressure will briefly drift through the area,
bringing lighter winds and cooler temperatures. Skies will
attempt to clear out over the high, allowing for better
raditional cooling and fog development. With the cool air mass
overhead, this also means temperatures dropping into the upper
20s, posing the risk for some freezing fog on Sunday morning.
However, the fog will be contingent on clear skies and light
winds, which are far from a guarantee with stubborn fall
stratus and a quickly moving high. The alternate scenario is
cloud cover holding on through the night, keeping temperatures a
bit warmer and farther from saturation. Increasing pressure
gradients and surface winds from the northwest will also work
against fog development, especially in the western portions of
the state. Therefore, it seems the highest likelihood of
fog/freezing fog on Sunday morning will be over the eastern
half of the forecast area, with diminishing probabilities
farther west.

&&

.DISCUSSION...
Issued at 229 PM CDT Fri Oct 31 2025

Upper low pressure is descending south through southern Minnesota
early this afternoon. Water vapor imagery and PV 1.5 pressure
analysis does show several distinct PV anomalies rotating around the
parent system with the lead anomaly east into Wisconsin while
another significant fragment is now rotating around the northwest quad
of the system. A broad stratus shield is accompanying the system and
that stratus extends northward and well into south central Canada.
Areas of precipitation are also occurring with a few concentrated
areas of rain with scattered showers in between to the north of the
state.

This entire system will move into Iowa overnight and into Saturday
then the area will gradually transition to cyclonic flow on the
backside of the system from north to south Saturday afternoon and
evening. Increasing clouds will lowering cloud bases occurring and
may areas may have a period with cloud bases below 1000 ft. The
first impact the thick stratus will have is on temperatures and
continued the trend of utilizing the NBM 25th for lows tonight
where the cloud cover exists. It is a bit tricky elsewhere where
some areas again may be near the NBM 25th pending on the
stratus arrival. Highs tomorrow will also be below guidance and
thus will maintain temperatures near the NBM 25th. Will continue
to note that most models continue to over mix the boundary
layer under the stratus thus the forecast temperatures are too
high. Have increased precipitation chances for the remainder of
today and through much of Saturday to account for the expected
showers. Low static stability associated with the main 1.5 PV
anomaly core (the northwest quad one) will move across the area
tonight. Shower chances will persist into Saturday and while
moisture depths will vary, there is modest low level instability
as well that will be conducive to shower development. If ample
low level saturation does occur, areas of drizzle could develop
as well with sufficient vertical ascent available within the
saturated layer for collision coalescence to occur. Based on
simple Iowa climatology with systems like this, the stratus
will likely last well into Saturday night. The current NBM low
temperatures are predicated on some clearing overnight so will
continue to monitor that situation. Should clearing occur, fog
will become possible and could become dense again, especially in
areas east of the return flow.

The return flow does arrive on Sunday and this should lead to warmer
albeit gusty conditions. Another system will pass through Sunday
night into early Monday. Perhaps light precipitation occurs over
northern Iowa but overall moisture is limited with this system. The
upper flow then transitions to the more classic westerly/zonal flow
which will bring warmer than normal temperatures and mostly dry
weather.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 631 AM CDT Sat Nov 1 2025

MVFR to IFR conditions prevail this morning as stratus drifts
overhead. Occasional light rain and drizzle has been drifting
through as well, especially over northern Iowa. This light
precipitation is expected to continue drifting south and east
through the morning, potentially persisting into the afternoon
as well. However, confidence is lower in afternoon rain, so have
left out of TAFs at this time.

Stratus should begin to lift and break up this evening,
although will want to see how stubborn it is in dissipating. If
skies do clear out tonight, fog and potentially freezing fog
may develop Sunday morning. However, due to some competing
factors, predictability for fog is low at this time. Will be
monitoring trends closely as we get closer to tomorrow morning.

&&

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

&&

$$

UPDATE...Dodson
DISCUSSION...Donavon
AVIATION...Dodson