195
FXUS63 KDMX 070438
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1038 PM CST Thu Nov 6 2025

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

.KEY MESSAGES...

- Breezy and seasonally mild this afternoon and again Friday. A
  few light showers and possibly thunderstorms southeast this
  evening.

- Precipitation spreading from west to east across Iowa on
  Saturday. Rain likely south, snow north, and a mix in between.
  High confidence in occurrence and timing of precipitation. Low
  confidence in precipitation type and any resulting snow
  accumulations.

- Much colder from Saturday night into early next week. Highs
  Sunday only around freezing, with lows Sunday morning and
  Monday morning in the teens and 20s.

&&

.DISCUSSION...
Issued at 129 PM CST Thu Nov 6 2025

Synoptic 500 MB analysis reveals a large gyre spinning over Hudson
Bay, with a series of troughs moving into and across the
northwestern U.S. in an otherwise roughly zonal flow pattern. The
first broad trough is crossing the northern U.S. Rockies and High
Plains this afternoon, and is comprised of two embedded shortwaves.
The leading wave is approaching Iowa at this time from South
Dakota/Nebraska, spreading mid/high level clouds toward our forecast
area, while the second is lagging over Montana and southwestern
Canada and will reach Iowa on Friday morning. As the initial
shortwave moves overhead this evening and tonight, preceding low-
level warm air/moisture advection and broad forcing for ascent will
eventually allow some showers to form, however by the time that
occurs it will mostly be east of our area over eastern Iowa and
Illinois/Wisconsin tonight. That being said, there is a window for
the first light showers to develop in our eastern/southeastern
counties this evening before quickly moving out, and thus have
maintained low (mostly 20-40%) PoPs in that area this evening until
midnight. Also introduced mention of isolated thunderstorms as short-
term guidance has trended toward some weak instability in our
southeast for a few hours around/after sunset. As the second 500 MB
shortwave then moves over on Friday, effectively bringing up the
rear of the broader trough within which it is embedded, it will
provide another shot of forcing that some model solutions are
deeming sufficient to generate a few light showers in our
northeastern counties around Friday afternoon. Forecast soundings
indicate there will be more substantial low-level dry air to
overcome at that time however, so have left the forecast dry for
now. Any rain that may occur would be very spotty and light and
of no impact.

By Saturday morning a sharper and more energetic 500 MB trough and
vorticity maximum, whose progenitor is currently sitting off
the coast of British Columbia, will move southeastward over the
western Dakotas and subsequently cross Iowa and Missouri
Saturday into Saturday night. Meanwhile, as the Hudson Bay gyre
continues to sit and spin, perhaps drifting down into far
northern Ontario, a pronounced trough will swing around it and
approach the Canada/U.S. border around International Falls by
midday Saturday. This feature will eventually reach Iowa on
Saturday night, hot on the heels of the preceding trough moving
in from the west earlier in the day. The net result of this
scenario will be precipitation spreading across Iowa on
Saturday, associated with the first trough, followed by much
colder temperatures and perhaps a second bout of lighter
precipitation surging into the region Saturday evening/night in
association with the second/northern trough.

The precipitation on Saturday is problematic and potentially
impactful due to the colder temperatures working into the area. As
the mid/upper trough moves overhead, an associated surface low will
move right along or just south of the Iowa/Missouri border. Around
the northern hemisphere of this low a deformation zone will pivot
over our forecast area, with ribbons of frontogenetical forcing
moving overhead and enhancing the broad lift accompanying the
trough. This will provide more than enough support for saturation of
the column and widespread precipitation, spreading from west to east
during the day, before the forcing cuts off after the low passes by
around late afternoon or so. Forecast soundings unanimously depict a
deep saturated layer well below freezing, with lift concentrated
within that layer and supporting generation of snow during the day.
In fact, most deterministic model solutions paint a transient
bullseye of forcing within the Dendritic Growth Zone, indicating the
potential for a few hours of high-rate snowfall production aloft.
The bugaboo is wet-bulb temperatures within the surface layer, and
whether they remain warm enough and deep enough to melt the falling
snow and result in more rain than snow at the surface. Most
solutions depict the near-surface warm layer as very shallow, with
surface wet-bulb temperatures cooling during the afternoon as the
heaviest precipitation falls which is consistent with the
traditional "dynamic cooling" scenario. However, with this period of
heavier precipitation potential/dynamic cooling reaching central
Iowa around midday it will be fighting diabatic heating and the
admittedly weak solar insolation maximum, so the p-type
forecast is very uncertain in that area. Confidence in snowfall
is higher across our northern counties where wet-bulb
temperatures will initially be lower and more difficult to warm
above freezing, which is also consistent with climatology. Have
continued the trend of cooling temperatures during the day
Saturday below NBM guidance, with a blend toward the NBM 25th,
NAM, and ConsAll, and also bumped dewpoints down a couple of
degrees during the heaviest precipitation window to lower wet-
bulb temperatures farther. While the official forecast does not
indicate measurable snowfall accumulations except in our
northern counties, there is certainly the potential for more
widespread impacts if cooler/snowier solutions prevail, and this
possibility will be closely monitored leading up to the storm.

All guidance shuts off the forcing sharply around or shortly after
21Z on Saturday as the low begins to move away, resulting in
precipitation ending or becoming very light by the end of the day.
However, as the second trough discussed above surges down from the
north Saturday evening, it will bring a quick shot of secondary
forcing which admittedly will be weaker and with less moisture to
work with. Even so, this may still be sufficient to generate some
flurries or light snow into early Saturday night, and in fact the
NAM (which is by far the most bullish on this) indicates some
possibility of impactful snow showers moving through with the
secondary trough. For now, have added slight chance (20%) PoPs to
account for this potential. Barring the stronger NAM solution any
such light snow would likely have little impact, but if it able to
significantly reduce visibility or accumulate on roads then there
may be additional travel impacts after dark Saturday evening/night.

After the two troughs move through Iowa Saturday-Saturday night,
much colder air will surge across the region in northwesterly flow
from Saturday night through Sunday. Late Saturday night into Sunday
morning, the rapidly falling temperatures and gusty north northwest
winds may promote freezing of previously fallen snow/rain on some
surfaces and there is a possibility of icy roads as a result, which
may occur even well after the precipitation has ended as
temperatures fall into the low to mid-20s early Sunday morning.
Highs Sunday are now only in the low to mid-30s across the area, so
any ice or snow that has formed/fallen may not melt much even during
the day, depending on the degree of clearing that can occur. It will
remain cold Monday as a surface high pressure ridge moves over the
region, which may result in even colder lows Monday morning in the
teens across much of the area, followed by highs Monday afternoon
around 35-40 degrees. From Tuesday through the rest of next week
Iowa will reside beneath benign west northwesterly steering flow,
which should support quieter weather and a steady modification of
temperatures, with a return of more seasonal readings by
midweek.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1037 PM CST Thu Nov 6 2025

Clouds will continue to decrease into Friday morning, with
mainly high clouds at times expected for most areas. Into
northern Iowa however, ceilings lower into the afternoon and
especially the evening ahead of another system arriving into
the region as low clouds gradually move into the area by the
evening. Winds out of the west will turn more northwesterly
through the day, becoming breezy with gusts up to 20-25 knots
expected through the afternoon, before gradually decreasing late
in the forecast period.

&&

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

&&

$$

DISCUSSION...Lee
AVIATION...Bury