531
FXUS63 KDMX 211801
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
101 PM CDT Wed Oct 21 2026

.KEY MESSAGES...

- Dry and unseasonably warm weather to continue from Thursday
  through Saturday, with daily highs generally in the mid/upper
  70s.

- Breezy conditions develop Friday and Saturday, especially in
  northern and western Iowa. Somewhat elevated fire weather
  concerns may develop during this time.

- Rain and relatively cooler temperatures return to
  northwestern Iowa later this weekend and the remainder of the
  area early next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 101 PM CDT Wed Oct 21 2026

Currently, a mid/upper level shortwave is weakening and shunting
off to our northeast toward the Great Lakes region, while at the
surface Iowa resides within nebulous but broadly anticyclonic
flow. Any forcing for ascent is thus very weak and atmospheric
moisture is limited. The results of this setup are mostly sunny
skies, dry conditions, and light southwesterly winds making for
another glorious autumn day throughout our service area.

From tonight through Friday night, a 500 MB ridge will build
across the Midwestern states and in fact, be centered near the
western Gulf Coast and extend all the way up toward Hudson Bay.
At the surface, a large high pressure area will settle over the
Great Lakes during this time, resulting in persistent south
southeasterly breezes across Iowa. Initially, from this evening
into Thursday morning, the surface pattern will be more nebulous
allowing for very light/calm winds overnight. With mostly clear
skies anticipated and a pocket of enhanced surface dewpoints in
the lower 50s bleeding mainly into the northwestern half of
Iowa during the night. This is a recipe for fog potential,
though it is somewhat mitigated by a relative lack of
ground/vegetation moisture given the season and the length of
time since our last meaningful rainfall. Nevertheless, high-
resolution guidance has been trending toward increasing fog
potential and have introduced some patchy fog in our
northern/northwestern counties toward sunrise Thursday
accordingly. Short-term trends will be monitored overnight in
case the coverage or density of fog increases beyond current
expectations.

A large 500 MB cyclone will come ashore over the California
coast early Thursday, then move over northern Nevada and
adjacent Oregon/Idaho by Friday morning. The energy/vorticity
associated with this cyclone will then split, with some being
absorbed by a northern stream system moving across Canada, while
the remainder sinks into the U.S. Desert Southwest Friday night
and is blocked by the preceding and aforementioned central U.S.
ridge. On Thursday and Friday, a broad surface low pressure
trough will develop along the Northern High Plains in the lee of
the Rockies, roughly near the eastern Montana/Wyoming and
western Dakotas region. As this occurs, the pressure gradient
between the trough and the Great Lakes high will gradually
tighten and bring somewhat stronger winds across Iowa on Friday,
especially in our northwestern counties where the gradient will
be tighter. A continuing warming trend also supports high
temperatures in the mid/upper 70s both Thursday and Friday, and
combined with relative humidity falling into the 30-40% range on
Friday afternoon as well as the aforementioned increasing
winds, this may support modestly elevated fire weather concerns
on Friday. Finally, during this time broad warm air advection
aloft, along with increasing moisture and weak shortwave
impulses ejecting out of the 500 MB cyclone, will support some
intermittent showers over the High Plains but these should
remain northwest of our forecast area and our forecast remains
dry through Friday night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Issued at 101 PM CDT Wed Oct 21 2026

By Saturday morning a southern stream 500 MB low/trough will be
centered somewhere near the California/Arizona border. It will
then drift slowly east northeastward toward the central U.S.
over the weekend and into early next week. By Monday evening it
should be located somewhere roughly around Nebraska, but by
that time a second 500 MB cyclone will have come ashore over the
northwestern CONUS. As these two systems interact with each
other the details of their evolution become more uncertain, but
by Saturday night the surface trough discussed in the SHORT TERM
section above should be pushed across the Dakotas and lie in an
orientation parallel to the steering flow, roughly from the
central High Plains northeastward near the Iowa/Minnesota border
and into the upper Great Lakes. Frontogenetical forcing
associated with this increasingly baroclinic zone, beneath
modest but broad forcing for ascent aloft, will support
increasing rain potential near the boundary as we progress
through the weekend. Most of this potential will initially lie
north and west of our area, but POPs are introduced for our
northwestern counties beginning Saturday night and continuing
through Sunday night. The boundary/swath of rain will be slow to
progress any farther into Iowa until the main system/s move
through sometime between Monday and Tuesday. Given this overall
scenario, unseasonably warm conditions in place late this week
will continue through Saturday, with the approaching
trough/frontal zone/rain swath remaining northwest of Iowa
during that time, then be shunted steadily southeastward Sunday
and Monday, with daily highs likely more in the 50s and 60s by
Tuesday and Wednesday of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1216 PM CDT Wed Oct 21 2026

Mainly VFR conditions will prevail through the TAF period. Some
patchy fog will develop in northwestern Iowa by around sunrise
Thursday and will likely remain west of the TAF sites, with the
possible exceptions of KMCW and KFOD where a brief period of
MVFR visibility is included in the TAFs. This potential will be
monitored into tonight in case the probability/magnitude of
impacts at these sites changes.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...Lee