186
FXUS63 KDMX 172051
AFDDMX

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

.KEY MESSAGES...

- Line of storms moving from west to east through the area this
  evening. Damaging winds and embedded tornadoes are possible,
  especially in the northern half of the state. Locally heavy
  rainfall also possible.

- Additional, potentionally widespread severe weather expected
  again on Monday. All severe hazards are possible, including
  tornadoes, large hail, strong winds and heavy rainfall.

- Multiple rounds of efficient rainfall tonight and Monday night
  may lead to additional rises on rivers, particularly in
  southern Iowa. Flash flooding also possible in urban areas.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 342 PM CDT Sun May 17 2026

A surface boundary currently sits draped from west to east over Iowa
early this afternoon. In areas north of this boundary, cloud cover
has generally limited mixing and weaker winds aloft have prevented
gusty conditions thus far today. Farther south, breezy winds have
started to pick up and will continue to increase as the stronger
winds aloft push northward into the area. This boundary is expected
to lift northward through the afternoon and evening hours, bringing
these gustier conditions farther north in the state. Wind gusts up
to 40 mph are possible, although should generally be around 30 to 35
mph.

Later this evening, we are looking at yet another round of severe
thunderstorm potential. Warm moist air will advect northward with
the boundary through the afternoon, presenting a highly unstable air
mass to an approaching cold front from the west. Fortunately, a warm
layer aloft has generally kept a lid on the atmosphere today and
prevented any convection along the front so far. As this boundary
lifts northward, a few scattered showers and storms may develop
along it, but the capping generally appears to keep this
activity at bay. The main show will be with the frontal passage
later this evening, producing a roughly north to south oriented
line of storms moving from west to east through the area.
Instability ahead of these storms will be around 2000 to 3000+
J/kg, with a fair amount of shear maximized along the warm front
that will then be across northern Iowa. Given this storm mode,
the primary concern for our forecast area will be damaging
winds, as modeled reflectivity structures imply strong cold
pools being produced along this line through the northern half
of the state. HRRR and RRFS wind gusty output support this
potential for strong winds 60 to 75+ mph winds, especially as
storms initially arrive in northwestern Iowa this evening. In
addition, 30 to 40 kts of 0-3 km shear and 150+ J/kg of 0-3 km
CAPE ahead of the line of storms could support tornadoes
embedded within the line of storms, especially with any segments
bowing to the northeast. This will be most favorable as storms
initially arrive in the area and for the part of the line
closest to the warm front in the northern half of the state.
Waning shear and instability will cause the strong cold pools to
fall out of balance and become outflow dominant through the
night, which should diminish the tornado risk as the line passes
over our area. However, gusty outflow winds will still be
possible into the early morning hours.

While storms won`t be as severe farther south in the area, slower
storm motions as the front begins to stall in Iowa may lead to
prolonged periods of heavy rainfall through Monday morning. Should
this rainfall linger over areas that already saw multiple inches of
rainfall, particularly far southern Iowa, we could be looking at the
potential for flash flooding and/or additional river rises. See
hydro discussion below for more information.

Overnight activity should generally wrap up by mid-morning on
Monday, but our days of perpetual thunderstorm chances will not yet
be finished. The atmosphere will work to recover ahead of an
approaching 500 mb wave which is slated to produce storms across the
area today. The synoptic support on Monday will be far more robust,
leading to a highly dynamic scenario. That said, leftover mesoscale
features from tonight will still play a role in how storms play out
Monday. Of course, atmospheric recovery will be important, but this
seems fairly likely by the time storms are expected to start in the
late afternoon/early evening. The other factor will be where the
cold front ends up on Monday. Right now, this is depicted to be over
western Iowa, but very well could move depending on the strength of
the MCS tonight. Regardless, of these features, it still looks
likely we will see strong storms on Monday. Assuming the atmosphere
recovers, some models indicate 4000+ J/kg of surface based
instability and 40 to 50 kts of deep layer shear developing ahead of
the cold front over central Iowa Monday afternoon. As the front
progresses eastward, storms will fire along it, taking advantage of
the loaded environment in Iowa. 300+ m2/s2 of 0-3 km SRH will
be available to storms with large looping hodographs. This
environment will be conducive for all severe modes, including
damaging winds, large hail and tornadoes. SPC has an enhanced
risk (level 3 of 5) for severe weather over much of southeastern
into central Iowa, with a 10% chance for tornadoes some of
which could be strong (reasonable max up to EF-2). A moderate
risk (level 4 of 5) is displaced just to our southwest where the
best tornadic potential resides Monday afternoon. Finally,
widespread storms across the area with plenty of moisture
available from the low level gulf moisture stream will bring
another round of heavy rainfall on Monday. This activity should
be progressive enough to avoid long residence times over a
particular area, but could produce efficient rainfall leading to
more water being added to rivers in Iowa.

It is worth mentioning, however, that both HRRR and RRFS output from
this morning have not been recovering the atmosphere as well on
Monday, leading to more convective inhibition than is being
indicated by the coarser models. This lack of surface based
instability would reduce our risk for tornadoes across the area,
should that scenario play out. Storms would still occur with plenty
of MUCAPE around, but they would be more of the elevated flavor.
This degree of destabilization will certainly be something worth
watching as we get through tonights storms and especially into
tomorrow morning.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 342 PM CDT Sun May 17 2026

A much needed break from the active weather stretch begins on
Tuesday as a high pressure nudges into the region later Tuesday into
Wednesday. Mid-level winds behind the departing system Monday night
also turn out of the north to northwest ushering in cooler
temperatures with highs in the 50s to 60s on Tuesday through
Thursday and lows Wednesday and Thursday mornings in the upper 30s
to 40s. Winds on Tuesday will remain elevated through much of the
daytime with a tight pressure gradient still in place with sustained
winds out of the northwest 15-25 mph, and gusts to near 30 mph in
the northwest. Showers and thunderstorms then return to the forecast
from later Thursday into Friday as an upper trough crosses the
Central Plains with a developing surface low reaching towards the
area into Friday. Additional details to come in the next several
days.

&&

.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.

&&

.HYDROLOGY...
Issued at 342 PM CDT Sun May 17 2026

The next two rounds of rainfall (this evening and Monday evening)
will have ample moisture accessible to them thanks to a healthy gulf
moisture stream up through the central U.S. Precipitable water
values both tonight and Monday night will be nearing 1.6" to 1.7"
(90th percentile for May 17th in Iowa is 1.27" and max is 1.6").
This suggests that anomalously moist air will be in place over Iowa
as these storms move through, leading to efficient rainfall with
both rounds. Fortunately, storm motions appear fairly
progressive for both events, which should help prevent prolonged
residence times. Rainfall amounts of 1 to 2" are possible with
some of the heavier storms. That said, there is some concern
that as the cold front/outflow boundary stalls over Iowa late
tonight into Monday morning, LLJ induced showers and storms may
persist over southern Iowa/northern Missouri for some time into
the morning. This could lead to some locally higher rainfall
amounts of 3" or more in these areas.

This is notable, as southern Iowa picked up the most rainfall
yesterday as well, and a poorly placed swath of additional rain
could exacerbate conditions along the Thompson and East Nishnabotna
rivers. These rivers are typically a bit faster at routing water
out, but full recovery is unlikely by tonight and rain could lead to
additional rises. Likewise, soils in these areas are likely already
saturated and crops are not to the point where they can help absorb
water, leading to some flash flooding concerns as well. This is all
contingent on if another swath of heavy rain lines up in these
areas, but certainly something to keep an eye on tonight and again
Monday night. Elsewhere in the state, urban areas will likely
be most susceptible as soils in rural areas still remain on the
drier side. However, with two potentially widespread rainfalls
tonight and tomorrow, will be keeping an eye on where the
heaviest rains set up. Should the same area be hit twice,
ponding or flash flooding could develop. The weather prediction
center has a marginal risk for excessive rainfall today and a
slight risk for excessive rainfall tomorrow, likely due to the
two back to back rainfalls.

Finally, in terms of river flooding, the perpetual rounds of storms
should end by Tuesday, but could see rivers responding through the
week, again depending on where the heaviest amounts fall. This will
be something better assessed in the coming days.


&&

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

&&

$$

SHORT TERM...Dodson
LONG TERM...05
AVIATION...Dodson
HYDROLOGY...Dodson