528
FXUS63 KDMX 152337
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
537 PM CST Mon Dec 15 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Fog is likely tonight into Tuesday in areas with snow on the
  ground. There is some potential for dense and/or freezing fog,
  at least in patches.

- Milder temperatures are forecast Tuesday and Wednesday.
  Additional fog is possible Tuesday night into Wednesday
  morning.

- A band of light rain will move through the area late Wednesday
  night into Thursday morning, followed by cooler temperatures
  and gusty winds on Thursday. Some icing could occur on roads.

&&

.DISCUSSION...
Issued at 216 PM CST Mon Dec 15 2025

Weak ridging has built over the region today, with modest west
southwesterly surface breezes across most of Iowa. This has
helped temperatures warm into the 30s and melting of the snow
pack has just begun. Some thin high cirrus clouds are streaming
overhead, but otherwise mostly clear skies are anticipated
tonight and winds will become lighter, still from the southwest
but closer to 5 KT overnight. With dewpoints in the 20s
currently being advected into the area and snow melt adding
near-surface moisture, this is a solid setup for fog development
after sunset tonight and into Tuesday morning in portions of our
area with snow coverage. However, there are some flies in the
metaphorical ointment. The first is the aforementioned cirrus
clouds, but these should be intermittent and remain high and
thin, so any mitigation of radiational cooling will be minor.
The second and more inscrutable impact is the degree to which
snow melting actually occurs today. Visible satellite imagery
indicates any erosion along the southern edge of the snow pack
has been very slow to develop, and over most of the snow area
air temperatures are still only in the upper 20s even at 2 PM.
This may limit the degree of water vapor introduction in the
near-surface layer. The third is uncertainty over winds will
really go calm (or nearly calm) or remain organized though
light. Given these competing factors, have expanded coverage of
fog in the forecast and messaging of its potential impacts, but
do not have sufficient confidence in widespread, dense fog
occurring, or ice accretion occurring on roadways, to issue an
advisory at this time. This potential will be closely monitored
this evening and tonight.

On Tuesday southwesterly winds will pick up again and
temperatures will rise even higher, peaking in the upper 30s to
around 40 over the snow pack, and well into the 40s in our
southwestern counties where the ground is bare. This will
promote additional, and likely more substantial, snow melt and
support potential fog development again Tuesday night into
Wednesday morning. It does appear a weak surface high pressure
area will move through around sunrise Wednesday which may cause
winds to go more calm and enhance fog potential. This will be
further assess tomorrow, once we have some data from the first
round of fog tonight. Wednesday will then be very similar to
Tuesday, once again mild but becoming breezier in the
afternoon, before the next weather system approaches Wednesday
night.

By Wednesday evening an energetic 500 MB trough/low will be
moving eastward along the Canada/Montana border, and will
subsequently deepen and dive southeastward Wednesday night,
crossing Iowa and neighboring states on Thursday. This will push
a surface cool front across the region, and along the front
low-level convergence beneath broad forcing for ascent will
support a wide band of rain moving across our forecast area late
Wednesday night into Thursday morning. Seasonally limited
moisture content and the progressive nature of the rain band
will keep amounts light, generally around a tenth of an inch,
and no impacts are anticipated initially. However, behind the
front temperatures will fall during the day on Thursday and
gusty winds will surge in, enhanced by a tight surface pressure
gradient and good cold air advection/low-level mixing, and the
winds and falling temperatures could freeze overnight rain on
roadways, leading to slick travel conditions. In addition, as
the core of the 500 MB trough/low moves overhead around Thursday
afternoon, the associated forcing may generate some snow
showers. Right now the probability of accumulating precipitation
is low, but if any snow does reach the surface it could
compound road condition concerns. All in all Thursday will be
blustery, damp in the morning, and travel considerations will
need to be monitored in the coming days.

From Friday onward the steering flow becomes roughly zonal and
the synoptic pattern supports generally dry and quiet
conditions, with alternating weak surface ridges and troughs
keeping temperatures moderate. The seven day forecast is dry
after Thursday as a result, with daily high temperatures varying
from the upper 20s to the lower 40s.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 537 PM CST Mon Dec 15 2025

Expecting fog to develop by late tonight and remain through much
of Tuesday morning, which is expected especially over the
northern terminals, and less so further south at KDSM while
looking least likely at KOTM. Main impacts would be lower
visibilities around 1-2 miles, though lower ceilings from clouds
moving in overhead could limit fog somewhat but still lead to
IFR and even LIFR at times. Trends will continue to be monitored
over the next several hours. Winds increase by late morning into
the afternoon Tuesday out of the southwest, with a frontal
passage gradually shifting winds northwesterly at the end and
beyond the current TAF period.

&&

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

&&

$$

DISCUSSION...Lee
AVIATION...Bury