582
FXUS63 KDMX 041727
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1227 PM CDT Sat Oct 4 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Elevated fire weather concerns remain this weekend,
  particularly for field fires with windy, dry, and warm
  conditions both days. Any spark could cause a fire, which
  could spread quickly!

- Unusual early October warmth continues along with dry weather
  through today if not much of the daytime Sunday.

- Increasing chances for scattered showers and storms into
  Sunday evening through early Tuesday. No strong signal for
  severe weather.

- Cooler next week with more seasonal conditions.

&&

.UPDATE...
Issued at 357 AM CDT Sat Oct 4 2025

Another quiet early morning across Iowa, with warm overnight
temperatures in the 60s to low 70s under mostly clear skies.
Synoptically, little change has occurred since this time yesterday,
with ridging over the eastern CONUS with the western extent of
surface high pressure covering much of the state, while a large
trough continues to gradually pivot northeast across the western
portion of the CONUS, as an area of surface low pressure is
currently centered over the Dakotas. As this trough continues to
deepen and lift across the Midwest today, the tightening pressure
gradient and increasing low level southwesterly flow is still
expected to result in increasing winds through the morning and
especially into the afternoon. Mostly sunny skies skies with
temperatures warming into the upper 80s to low 90s will result
in good mixing to occur, allowing 850mb winds around 35- 40+
per deterministic model guidance to likely mix down to the
surface, with highest values into northwest Iowa. This mixing
will also lead to lower dewpoints in the low to mid 50s and
therefore lower RH values as they fall into the 30s across
central Iowa. These warm, dry and windy conditions will lead to
elevated fire weather concerns, focused primarily on cropland
given very high to extreme cropland danger index values across
the state, and less so for grasses as they generally were
reported as being less dry at this point in the season. After
much coordination between neighboring Iowa offices, have put out
a Special Weather Statements for the entire CWA highlighting
the elevated fire danger in cropland this afternoon to early
evening. Extra care will be needed to avoid sparks from
machinery, and avoid burning of any kind as fire starts will
easily spread. Conditions improve this evening, with RH values
increasing above 50% and winds decreasing, while overnight lows
fall into the 60s.

Relatively strong low level southwesterly flow remains through
much of Sunday, which will allow for another day of breezy
conditions, with gusts up to 25-30+ mph through the afternoon
and decreasing into the evening. Though winds are a bit less, RH
values will largely drop into the upper 30s, with temperatures
through the 80s leading to another day of elevated fire danger
for cropland. Clouds increase into the afternoon as a more
defined shortwave impulse lifts northeast within the larger
trough into the Upper Midwest Sunday, with a northeast to
southwest oriented boundary moving into Iowa. This will be
paired with increasing moisture over the same area that will end
the streak of dry conditions, with showers and storms expected
late Sunday afternoon to evening. As the low level jet increases
into the evening and overnight into Monday however, better
forcing will lead to a higher likelihood for more productive
rainfall. Given marginal shear and instability values below
500 J/kg, the concern for severe weather is low. Winds begin to
shift across the northwest portion of the state late Sunday
into Monday, becoming northerly behind the boundary.

This boundary per guidance generally weakens through the morning to
afternoon Monday given the weaker forcing, leading to more
spotty showers and storms, but the boundary itself will be very
slow to depart, remaining at least overhead across at least
southern into south-central Iowa Monday evening into Tuesday.
The low-level flow at this time will be much weaker, limiting
forcing though some rain shower development should re-develop
over the area during this time. Rainfall totals by Tuesday
morning per GEFS guidance has totals generally around 0.75
inches across central to southern Iowa, with amounts around to
just above an inch in southwestern Iowa.

&&

.DISCUSSION...
Issued at 225 PM CDT Fri Oct 3 2025

It is a warm Friday afternoon across Iowa with just a few clouds in
southwest and southeast Iowa. More broadly, there is little in the
way of an area of substantial clouds over much of the eastern and
central US as these reside beneath the now again dominate mid-level
ridge and surface high pressure. GOES-East upper level water vapor
imagery shows that a sharp, amplified trough has moved over the
western US. This trough will move eastward and then northeastward
this weekend with surface cyclogenesis over the central Rockies.
With the high pressure to the east of Iowa and low pressure
developing to the west, winds will increase as the pressure gradient
tightens. Winds are just a bit breezy this afternoon, mainly over
western Iowa, but there is a lack of stronger winds at the top of
the mixed layer to tap into and mix to the surface. That won`t be
the case on Saturday as winds in the low levels will be stronger,
especially from Nebraska into Minnesota clipping northwest Iowa, and
this raises the concern for elevated fire weather conditions in
cropland. Cloud cover is expected to be at a minimum with perhaps a
few high-level cirrus clouds passing over in intervals in the
afternoon per latest HREF. With near full sunshine expected, deep
boundary layer mixing is anticipated. Pick your model forecast
soundings show this warming and drying that deepens the boundary
layer up to 7000 feet or so. Thus, the stronger low level winds at
the top of the mixed layer around 40 knots in western and parts of
northern Iowa should be able to be mixed to the surface with surface
gusts of 30 to 40 mph common with a few gusts over 40 mph in a few
places. Even warming and mixing in drier air at the surface, surface
dewpoints remain in the 50s with relative humidity staying largely
above 30%, though a few spots may drop into the upper 20 percents.
Calling around to fire weather partners yesterday and today, the
consensus in our service area is that grassland fuels remain green
enough to not warrant a Red Flag Warning/concerns of rapid grassland
fire spread. However, cropland in many areas is dry with the
cropland fire danger showing very high or extreme in central Iowa in
the warm and windy conditions. With harvest in full progress, the
concern is for field fires that develop and spread rapidly in these
conditions and keep fire departments busy. We will continue to
message this concern in our public facing forecasts and likely issue
a Special Weather Statement focused on the cropland fire danger
Saturday morning in conjunction with at least some of our
neighboring offices.

Winds will diminish into Saturday night and relative humidity will
rise ending this round of elevated fire weather conditions. Through
Sunday, the upper level trough and associated surface low will lift
through northern Minnesota into the southern Manitoba and Ontario
provinces. With the stronger low level flow and pressure gradient
moving away from the state on Sunday, winds won`t be quite as
strong, but will still be quite breezy. So, another day of elevated
fire weather conditions will once again be present with very high
cropland fire danger. In addition, cloud cover is expected as a
surface cold front - attached to the departing low - is dragged
through the state. This will yield a slightly less warm day with
highs in the low and middle 80s. As stronger low level QG
convergence arrives and waves of theta-e advection pass over the
state, scattered showers and thunderstorms should develop in the
afternoon if not Sunday night in most areas with the exception being
parts of northwest and north central Iowa that may miss out on much
of this rainfall. Nothing has changed in the parameter space or
AI/ML guidance to suggest a strong setup for severe weather given
the marginal at best instability and largely out of phase shear.

Moving into early next week, conditions will be more seasonal with
highs in the upper 60s or low 70s through at least midweek. The
front that looked to somewhat stall south of the state is more
progressive in today`s deterministic guidance. There will still be a
period of scattered showers and storms in the wake of this front as
QG convergence lingers and weaker waves of theta-e advection pass
over Iowa Monday through early Tuesday. With the expected more
progressive pattern, deterministic guidance not surprisingly has
lower QPF generally between 1 and 1.5 inches. National Blend of
Models probability of an inch or more of rainfall in this period
focuses the highest probabilities at 20 to near 40% over the
southern half of the state. Any rainfall will be welcomed by the
recent stretch of dry weather that has soils showing at or below the
30th percentile in many areas.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1227 PM CDT Sat Oct 4 2025

Winds across Iowa are gusting 25-35 kts this afternoon with
highest gusts in northwest Iowa. This evening winds will ease
at the surface as daytime heating is lost and the inversion sets
up. This will result in LLWS across all sites. By Sunday
morning daytime mixing returns, washing out the inversion and
bringing back gusts of 25-35 kts.

&&

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

&&

$$

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