278
FXUS63 KDMX 171747
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1247 PM CDT Sun May 17 2026

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

.KEY MESSAGES...

- Early morning rain tapers off across the area by around 10am,
  then becoming warm, dry, and breezy. Wind gusts of 35-40 mph
  possible through the afternoon.

- There is an Enhanced Risk (level 3 of 5) for severe storms
  this evening. Strongest storms are expected in western Iowa
  with a line that will move across Iowa in the evening and
  overnight into Monday morning. Tornadoes, damaging wind, and
  large hail are all possible with this line of storms.

- The final day of severe weather in this active stretch is
  Monday with another Enhanced Risk (level 3 of 5) for severe
  storms. Storms are expected to develop in southwest Iowa late
  in the afternoon and move across Iowa through the evening.
  Tornadoes, damaging wind, and large hail are all possible with
  this line of storms.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 232 AM CDT Sun May 17 2026

Storms early this morning have settled across southern Iowa with an
area of strong wind gusts occurring north of the line with
drying north of the precipitation shield. Gusts of 55-65 mph
were reported, but have diminished early this morning.
Meanwhile, an MCS moving across Nebraska and Kansas has reached
far western Iowa. It has diminished in strength this morning and is
expected to continue to weaken as it moves across the southern half
of Iowa this morning. Precipitation is expected to taper off quickly
from 7-10am. It then becomes very warm, dry and breezy through the
rest of this afternoon. Soundings continue to indicate mixing
through dry low levels with wind speed of 35-45 kts at times at the
top of the mixed layer. While these higher gusts may not make it to
the surface, gusts of 35-40 mph are possible through the afternoon.
These winds are owed both to the mixing and dry air at the surface
and the tightening pressure gradient across the state as the surface
low lifts north through the plains and midwest.

The surface low sets up across Nebraska and South Dakota by late
this afternoon with convection firing in the vicinity of the triple
point and south along a trailing boundary. The environment across
Iowa ahead of the incoming boundary is ripe for severe storms. This
will be a nocturnal setup for Iowa as storm reach western
portions of the area around 02z and push across the area
overnight, exiting east close to 10z. Strongest storms are
expected west with diminishing strength as the line propagates
east overnight. The 00z HRRR sounding at Estherville tomorrow
evening at 02z provides a snapshot of the conditions available
for storm as they move into the area. The environment is deeply
unstable with 2500-3500 J/kg of SBCAPE and mid level lapse rates of
8C/km. Stretching through the low levels is there with 100-150 J/kg
of 0-3 km CAPE. Hodographs are also favorably curved with streamwise
values of 0.029 (this is pretty high). 300- 500 m2/s2 of 0-3km SRH
will favor sustained rotating updrafts with 400+ m2/s2 at the 0-1km
layer and even 300 m2/s2 for 0-500m. This is more than sufficient
for tornadogenesis and could support strong and/or long lived
tornadoes. This does not guarantee that scenario will occur, simply
that the environment would support it in western Iowa. DCAPE values
are also 1000-1200 J/kg. All of this is supportive of strong
convection as the cells in northwest Iowa begin to grow upscale into
a line as it moves east. This would be capable of tornadoes, large
hail, and damaging wind gusts. Storms are expected to diminish in
strength towards 06z and fully exit the area around 10-12z based on
current CAM trends.

With storms exiting the area early there should be plenty of time
for recovery through the day on Monday. This is the final day of
severe weather in this active period as the upper level trough
finally lifts up out of the area. The upper level support will
create a more dynamic setup and has the potential to be the
most robust day of severe weather of the period. Reflecting
this, there is an Enhanced Risk (level 3 of 5) across Iowa with
a Moderate Risk (level 4 of 5) just to the southwest of Iowa. We
will have to watch the track closely as convection from tonight may
influence changes to the track on Monday afternoon and evening. As
it currently stands, storms are expected to develop in far southwest
Iowa late Monday afternoon, growing upscale into a line of storms
that pushes across Iowa through Monday evening. All hazards are once
again expected including tornadoes, large hail, and damaging wind
gusts. The environment once again includes 2500-3000 J/kg of SBCAPE
with 300+ m2/s2 of 0-3 km SRH and 200+ m2/s2 0-1 km SRH (150+ m2/s2
0-500m), mid level lapse rates of 8C/km and 1000+ J/kg DCAPE. In
addition to the severe storms risk, the hydro risk continues after
repeated days of convection across the state. The progressive nature
of both Sunday and Monday convection should help to mitigate more
widespread problems, but it will be worth monitoring for areas that
may be vulnerable.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 330 PM CDT Sat May 16 2026

The encore system will lift through the area on Monday, bringing the
potential for widespread storms and heavy rainfall. Severe weather
looks likely with this system, as the parameter space boasts 60+
dewpoints, very unstable, surface based conditions, and a good
amount of kinematic support along the cool front passing west to
east through the area. All severe hazards will be possible,
including hail, damaging winds and tornadoes. Strong moisture
transport will also lift into the warm sector of the Monday system,
bringing plenty of liquid into the area. Storms should be fairly
progressive along the cold front, but localized ponding or flash
flooding is certainly possible, especially in areas that receive
rainfall tonight and Sunday night as well. Likewise, more water
being added to local rivers could lead to in-bank rises through next
week. We then see a brief break in the active pattern through the
middle of the week, with milder temperatures overhead.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1241 PM CDT Sun May 17 2026

MVFR conditions are impacting much of the area today, as clouds
around 1.5kft to 3kft span much of Iowa. These will likely
linger into the afternoon, although daytime heating should help
lift the ceilings, especially south. Winds have stayed lighter
over northern Iowa where more cloud cover has been present,
but are quite breezy farther south near KDSM and KOTM. Winds
will remain breezy (south) or increase (north) through the
afternoon and into the evening. Scattered showers are possible
near KFOD, KMCW, and KOTM later this afternoon, before a roughly
north to south oriented line of stronger storms moves from west
to east across Iowa around 02z and beyond, impacting all sites.
Strong winds and lowered ceilings may accompany these storms
overnight, before moving out into the early morning. LLWS may
also develop overnight, primarily at KDSM and KOTM.

&&

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

&&

$$

SHORT TERM...Hagenhoff
LONG TERM...Dodson
AVIATION...Dodson