866
FXUS63 KDMX 171137
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
637 AM CDT Fri Oct 17 2025

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

.KEY MESSAGES...

- Breezy south-southeast wind today with gusts of 20-30 mph expected.

- A line of showers will slowly pass across the area today from
  northwest to southeast. A few rumbles of thunder are possible
  however the severe threat is low.

- Saturday will be breezy once again with precipitation chances
  return in the afternoon and evening.

- Cooler Sunday through next week with precipitation chances
  returning mid to late week.

&&

.UPDATE...
Issued at 252 AM CDT Fri Oct 17 2025

The western US trough has made it to the midwest early this Friday
morning and cloud cover has expanded over much of Iowa. At the
surface, the low pressure center is located across North Dakota
with the surface cool front extending south into South Dakota
and Nebraska, just reaching the far northwest corner of Iowa as
of 2am. Light showers have developed associated with the
boundary and these will slowly move across the area from
northwest to southeast through the day. A thin ribbon of very
weak instability develops this afternoon with MUCAPE <500 J/kg
(a nose of ~1000 reaches far southern Iowa very late tonight)
and 0-6 km shear is around 30 kts (higher behind the boundary).
This may allow for rumbles of thunder and a few stronger storms
to develop, however the overall severe risk is quite low. Higher
severe chances are south of the area into Missouri with better
instability.

In addition to the rain chances today, winds will be breezy out of
the south to southeast with the tightening pressure gradient ahead
of the trough axis and warm air advection into the area. Moist air
in place will prevent deeper mixing, however model soundings
still indicate 25+ kts through the mixed layer.

Saturday will start off dry and be another breezy day with gusts of
20-25+ kts through the mixed layer. By afternoon a reinforcing lobe
of vorticity drops south across the area, bringing another
round of showers across the area through the afternoon and
overnight. With even less instability to work with, expect
nothing stronger than a few rumbles of thunder. With the trough
axis finally through the area Saturday evening, temperatures
Sunday will be much cooler, only warming into the low 60s. With
a much drier airmass in place on Sunday relative humidity will
drop under 35% and combined with breezy conditions may result in
increased agriculture fire weather concerns.

&&

.DISCUSSION...
Issued at 244 PM CDT Thu Oct 16 2025

On and off rain showers and weak storms riding the large-scale ridge
continued across parts of central to eastern Iowa this morning,
though the increasing warm air advection into the state through the
day has elongated the ridge vertically to the north, pushing these
showers out of the state with dry conditions across Iowa this
afternoon. The increase in low-level southerly flow in the area,
along with a tightened pressure gradient overhead has brought breezy
winds, especially northern/western Iowa where gusts up to 25+ knots
have occasionally been reported so far today and will continue into
the early evening before decreasing slightly. This increase in warm
air advection has been warming temperatures over the region as well,
though there is a sharp difference in values as afternoon values
range in the mid to upper 70s across the southwest half of the
state, while the northeast is cooler in the upper 50s to 60s. This
is largely attributed to the clearing skies southwest allowing for
better warming, while further north and east still have lingering
low to mid-level cloud cover. These clouds will continue to lift
completely out of Iowa, and besides some occasional high clouds,
should see warming continue with highs expected to reach into the
mid 70s to low 80s, warmest southwest.

Looking further west, lee cyclogenesis has formed a large area of
low pressure centered over eastern Colorado into western
Nebraska/Kansas in relation to a large trough that has been
circulating over the western CONUS over the past few days now. This
low pressure system is expected to track northeast into the Upper
Midwest region this evening, particularly over the Dakotas into
Minnesota, keeping Iowa well within the warm sector and remaining
dry tonight into early Friday morning. Lows tonight are expected to
fall into the upper 50s to low 60s. A rather weak northeast to
southwest oriented frontal boundary from the aforementioned system,
along with a push of moisture into western Iowa will bring the next
chance for showers after sunrise Friday, tracking slowly eastward
through the day before stalling near east-central to eastern Iowa by
the evening. Following the weak frontal passage over most of the
state, temperatures will only be a touch cooler in the mid to upper
70s, while ahead of the front, values reach into the low 80s.
Guidance continues to indicate a better push of moisture into
east/southeast Iowa where the warmer air will be located by the
early evening, along with a gradually strengthening low level jet
that will result in a higher potential for showers and even storms
to develop. Instability present over the area, along with favorable
shear around or above 30+ knots will allow for at least a low chance
for a few strong storms. Looking further among models indicates a
variation in instability over south/east Iowa with the NAM/GFS
showing values under 500 J/kg, while the HRRR/RAP indicate higher
values around 500-1000 J/kg by Friday evening, which seems more
reasonable given the warm and moist environment ahead of the
boundary. The primary hazards with any strong storms, with even a
low severe risk, would be small hail and gusty winds. The SPC has
the area in a General Thunder outlook, though a Marginal Risk has
been introduced over a portion of far southern Iowa in the afternoon
update given the potential that currently exists. Something to
certainly monitor over the next several hours.

Showers and weaker storms look to linger over eastern/southern Iowa
into Saturday morning. Following a brief dry period through Saturday
afternoon for much of Iowa, a rather potent lobe of shortwave energy
within the larger circulation into southern Canada looks to pivot
down into Iowa Saturday evening, with another push of moisture into
eastern Iowa towards the Ohio Valley region and forcing for lift
which will result in the chance for redevelopment of showers and
storms over the same areas. Latest trends among guidance though seem
to keep much of this activity further south and east, with most if
not all activity near the boundary out of the state where the better
parameter space looks more likely to setup. However, weaker lift
into Central Iowa with lingering moisture along an ahead of an 850mb
cold front could bring a quick shot of light showers Saturday
evening. Lingering weaker showers may continue into early Sunday as
well, then conditions dry out across the region as dry air spreads
overhead with a large area of surface high pressure dropping
southeast across the western part of the Central Plains. This will
come with a rather strong push of northwesterly flow into Iowa that
will bring much cooler temperatures into the area, with highs
expected in the 60s. Breezy conditions with lower RH values in
the upper 20s to low 30s could lead to a potential for elevated
fire weather conditions as well. The dry conditions per longer
range guidance looks to hold into the start of the work week,
with a switch back o southwesterly flow ahead of another surface
low tracking eastward across the Upper Midwest, extending a
boundary into Iowa by Monday evening before departing Tuesday.
Per GFS, weak moisture and lift over the state keeps chances
mainly over north/northeast Iowa, though the Euro indicates more
extensive coverage across much of Iowa. Differences like this
are expected given this is several days out so will have to
watch, but not anticipating much impact in terms of significant
rainfall or storms at this time.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 637 AM CDT Fri Oct 17 2025

A line of showers will move across the area from northwest to
southeast through the day. Morning impacts at KFOD/KMCW,
shifting to afternoon at KALO/KDSM and this evening at KOTM.
Initial coverage will be very spotty and light so have opted for
PROB30 at most sites, except KOTM where confidence is higher
for impacts at the site and -SHRA is prevailing this evening. A
few rumbles of thunder are possible, but with lower confidence
in occurrence have kept from TAFs at this time. Winds today will
be breezy out of the south to southeast gusting 20-25+ kts
during daylight hours.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Bury
AVIATION...Hagenhoff