998
FXUS63 KDMX 061133
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
633 AM CDT Sun Sep 6 2026

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

.KEY MESSAGES...

- Isolated areas of patchy fog expected this morning.

- On and off showers and storms expected over
  western/southwestern half of Iowa later this morning through
  Monday morning. Gusty winds and heavy rain are the primary
  hazards of concern.

- Additional storm chances with a passing boundary late Monday
  through Tuesday, with some potential for severe weather over
  much of the forecast area.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 304 AM CDT Sun Sep 6 2026

Relatively quiet weather is ongoing early this morning, with mostly
clear skies overhead. Due to light winds and little difference in
temperature/dewpoint values in the 70s making for continued
uncomfortable nighttime conditions, isolated areas of patchy fog
have developed over portions of northern and eastern Iowa, where
lowest visibilities are around 3-4 miles. The expectation is that
little change in conditions should allow for some expansion of this
patchy fog coverage, mainly over northern and eastern Iowa, before
dissipating around/just after sunrise.

As fog dissipates around sunrise, a mid-level shortwave rounding the
apex of the persistent ridge overhead will allow for increased
forcing for lift into Iowa. This feature will interact with a
noteworthy instability gradient that is draped over the
west/southwest half of Iowa, which will be the focus area for
showers and storms to develop. While CAM guidance varies somewhat in
the evolution and timing of this expected convection, probabilities
are looking highest for storm development and increased coverage
over western/southwestern Iowa into the afternoon to early evening,
tracking southeastward with time. The environment overhead features
MUCAPE values around 2000-3000 J/kg, given higher moisture content
and temperatures into the mid to upper 80s, while lapse rates look
unimpressive around 6.5 C/km paired with shear values around 25
knots. While isolated in nature, there is a potential for strong to
severe storms at times with this on and off storm activity, with
highest chances in the afternoon to evening. Gusty winds would be
the main hazard of concern, with DCAPE values around 1000-1500 J/kg.
The signal is also increased for heavy rain with this activity,
given higher PWATS around 2 inches, warm cloud depths, and a skinny
CAPE profile. This shower and storm activity looks to decrease in
coverage into the evening, but could continue at times into Monday
morning given an increasing LLJ extending into far western Iowa.
Some model members suggest a decaying MCS dropping southward across
western Minnesota through the morning, but looks to dissipate
before reaching NW Iowa. This however will be something to keep
an eye on. Total rainfall amounts around an inch look to be
common by Monday morning near and west of I-35, though localized
2-3 inch amounts are certainly possible. Flooding concerns
should be minimal, with any potential mainly over urban areas if
rainfall can quickly accumulate.

Throughout the rest of Monday, the aforementioned ridge will
translate further eastward, with its location now more directly over
Iowa. This will allow for an increase in 850mb temperatures overhead
and therefore capping, as well as a lack of instability due to the
influence of the surface high over the Great Lakes to cut off any
additional shower and storm development. Dry conditions should be
common across the forecast area by the afternoon, with increasing
low level southwesterly flow allowing for breezy conditions, as
gusts up to 25-35 mph are expected, highest over northern Iowa.
Cloud cover will decrease at the same time, with forecast highs
through the 80s, warmest southwest.

By Monday evening, the ridge breaks down somewhat as a rather potent
trough and associated deepening surface low tracks eastward into
Manitoba. With this system, an attendant cold front extending down
into the Central Plains is forecast to enter northwest Iowa late
Monday evening into Tuesday morning, which will be the next focus
area for shower and storm activity to occur. At this time,
deterministic models suggest the development of showers and storms
to occur across northern Iowa through Tuesday morning, as an
increasing LLJ northward across Iowa will act to enhance lift along
the boundary, with notable warm air advection overhead. This
activity may wane a bit later in the morning with the decreasing
jet, but is suggested to develop additional convection later in the
afternoon to evening given peak heating and the gradual resurgence
of the LLJ late in the day further south. The airmass ahead of this
feature will be quite warm and humid, with temperatures expected to
top out through the 90s, paired with dewpoints in the upper 60s to
low 70s. This is an ideal setup for storms to become organized and
potentially turn strong to severe, with a Marginal Risk in place
over much of the forecast area per latest SPC guidance. Heavy rain
with this activity is also looking increasingly likely, given strong
moisture transport into Iowa. Additional details will be refined on
specific timing and coverage in future forecast updates. Forecast
heat indices back into the 100-105 range over portions of central to
southern Iowa before storms arrive will likely lead to additional
heat headlines in the near future, so stay tuned.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Issued at 239 PM CDT Sat Sep 5 2026

The flattening of the sub-tropical high will continue Wednesday with
a westerly/zonal flow for the mid to end of the week. Less certainty
late next week with spatial and temporal differences with the
next strong upper level short wave that will arrive into the
Pacific Northwest. This will determine how much the sub-tropical
high ridging can become re-established over the western CONUS
and the difference between seasonal westerly flow or cooler
northwest flow and attendant precipitation chances associated
with each.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 633 AM CDT Sun Sep 6 2026

Seeing patchy areas of low ceilings and fog across the majority
of terminals, leading to anywhere from MVFR to LIFR conditions
this morning. Conditions will slowly improve over the next 2-4
hours or so across all sites as ceilings lift and fog
dissipates. Otherwise, there remains the potential for on and
off showers and thunderstorms to impact KFOD after 16z, and
later this afternoon at KDSM as coverage of this activity
increases. However, confidence on exact coverage and timing
remains low-end, so have kept PROB30 mentions at this time and
will amend as needed as showers and storms develop through the
day. Winds out of the southeast will increase, with gusts up to
15-20 mph by the afternoon.

&&

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

&&

$$

SHORT TERM...Bury
LONG TERM...Donavon
AVIATION...Bury