Severe Thunderstorm Warning 72, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
620 PM CDT Wed Apr 15 2026

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Slight Risk for severe storms expended more to the west today.
  All modes of severe weather possible, with a locally higher
  tornado threat along the I-80 corridor.

- Enhanced Risk expanded for Friday, covering much of the
  eastern half of the state.

- Much cooler over the weekend with a hard freeze likely in
  northern Iowa Saturday night.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 130 PM CDT Wed Apr 15 2026

A nearly stationary frontal zone is draped across Iowa this
afternoon, with the surface boundary stretching from around
Glenwood to Des Moines to Elkader. South of the boundary, winds
are gusty from the south southwest and temperatures are soaring
into the 70s. North of the boundary, winds are light and
variable and temperatures are holding in the upper 50s to 60s. A
cluster of severe thunderstorms developed this morning in
eastern Nebraska and has tracked east northeastward into our
area, affecting areas between Highway 20 and Highway 30 and west
of I-35 so far. However, farther south near the surface boundary
the atmosphere remains undisturbed and very unstable, with
strong deep layer shear moving overhead. As a mid-level trough
approaches from the west this afternoon, it will generate
additional storms along and south of the surface front that will
carry an attendant threat for large hail, strong winds, and
perhaps a few tornadoes. The storms will eventually clear our
area to the east this evening, though a few weaker showers or
storms may bubble up behind it as the mid-level trough moves
overhead.

Later tonight through Thursday night, a 500 MB ridge will build
across the region and provide a brief respite of quiet weather.
Thursday will be mild and dry, with winds coming around to south
and picking up later in the day. The strongest winds will be in
our northwestern counties, farther from the departing ridge to
the east, with speeds of 15 to 20 MPH and higher gusts up around
Estherville and Storm Lake on Thursday afternoon. As
temperatures warm to near 80 degrees in that area, RH will
plummet to near or just below 30 percent, combining with the
gusty winds to result in an elevated fire weather risk, mainly
north of I-80 and west of I-35. On Thursday night relative
humidity will characteristically increase after sunset, however
winds will remain brisk through the night and support
unseasonably warm low temperatures by Friday morning.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 105 PM CDT Wed Apr 15 2026

By Friday morning a deep longitudinal 500 MB trough will be crossing
the U.S. Rockies, emerging over the High Plains late in the day. A
surface low pressure trough will develop ahead of this system,
stretching from around the Texas Panhandle northeastward across
Kansas, Iowa, and toward Lake Superior by the middle of the day. A
sharp baroclinic zone will develop along this trough, with gusty
south breezes ahead of it and stronger north northwest winds behind
it providing enhanced low-level convergence beneath a broad region
of dynamic lift on the leading flank of the approaching 500 MB
trough. Initially a low-level inversion will inhibit convective
initiation, but by the afternoon near-surface warming and mixing
will erode the cap and numerous thunderstorms will develop all along
the frontal zone. SBCAPE of 3000-3500 J/KG and 0-6 KM Bulk Shear of
35-45 KT will support strong updrafts and a severe weather threat
across a large area, particularly given the magnitude of forcing for
ascent. Forecast soundings indicate a deep unstable layer and strong
winds aloft (around 50 KT at 700 MB), but generally straight
hodographs with little directional shear in the effective layer. Any
surface-based storms will be able to tap into modest directional
shear in the lowest levels, but the tornado threat remains uncertain
due to a relative lack of backed surface winds - certainly any
storms moving to the right of mean motion would carry an enhanced
tornado threat. In any event, given the strength of the wind fields,
linear nature of the convection along the frontal zone, and
magnitude of instability in the hail growth zone, damaging wind
gusts and large hail appear to be the primary threat at this time.
If the storms are able to form an organized QLCS, then the tornado
threat may increase accordingly. Overall, any areas of Iowa that are
along or east of the front when convection initiates will see a
significant threat of severe weather on Friday afternoon and
evening. There is still some uncertainty in exactly where the front
will lie when storms develop, but the eastern/southeastern half of
Iowa appears most likely to be under this threat.

The cold front will sweep through on Friday night, ushering in
considerably cooler weather for the upcoming weekend. High
temperatures on Saturday will be about 25-30 degrees lower than on
Friday, ranging in the mid-40s to lower 50s across our forecast
area. Meanwhile, Friday night/Saturday morning lows will fall below
freezing in our northern and western counties, though strong post-
frontal winds should prevent any frost formation at that time. By
Saturday night/Sunday morning a surface high pressure area will be
building into Iowa from the northwest, sending temperatures lower
and also diminishing winds. Lows will likely range in the mid/upper
20s north to lower 30s southeast, resulting in a hard freeze in some
areas and potential frost across much of our service area, depending
on wind speed and cloud cover. A large-scale broad ridging pattern
will then set up from later Sunday into the first half of next week,
supporting a few days of quieter weather with a gradual warming
trend. There are some signs that a more active pattern may return
from around the middle of next week onward, but that will be
determined in the coming days.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 606 PM CDT Wed Apr 15 2026

Main concern in the next 6 hours will be the departing thunderstorms
at KOTM. KDSM and KALO could also seem some scattered storms, but
these will have less coverage. Some CAMs show scattered
-SHRA/-TSRA possible over northern IA this evening so added
PROB30s at FOD and MCW.

Otherwise, once the storms exit the region, a narrow ridge of
high pressure will build overnight. This will lead to clear
skies, and potentially some patchy fog. As of now, MVFR fog
looks most likely at ALO where residual moisture from this
evening's storms will aid in surface saturation. On Thursday,
expect VFR conditions with increasing southerly winds with
sustained values near 10 kts toward the afternoon.

&&

.HYDROLOGY...
Issued at 119 PM CDT Tue Apr 14 2026

Multiple rounds of seasonally moderate to heavy rain this week will
lead to renewed flooding concerns. Concerns will include possible
renewed or additional river flooding as well as flash flooding.

Output from the GFS- and NBM-forced medium-range National Water
Model (NWM) and the Hydrologic Ensemble Forecast System (HEFS)
suggest the most likely scenario will be moderate to significant
within-bank rises on many rivers and streams across the CWA over the
next week, especially across the southeast half. Some locations may
see minor river flooding as well. These rises will be due to the
additive effect of multiple rounds of rainfall. If rainfall is
higher than presently forecast then the risk of several locations
seeing minor flooding and a few locations seeing moderate flooding
will increase.

Flash flooding is less of a concern than river flooding, however the
risk is nonzero. The additive effect of rain events will result in a
slightly higher risk of flash flooding from Friday into Saturday.
The most likely scenario through the end of this week will be
ponding of water or low-end flash flooding especially in urban areas
or areas that receive repeated heavy rainfall over a relatively
short time period.

&&

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

&&

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...
HYDROLOGY...Zogg

Hazardous Weather Outlook
National Weather Service Des Moines IA
411 AM CDT Wed Apr 15 2026

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-160915-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
411 AM CDT Wed Apr 15 2026

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

There is a Slight Risk (Level 2 of 5) for severe thunderstorms
across much of Iowa this afternoon and evening. Damaging winds,
large hail, tornadoes, and flash floods are all possible.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

There is an Enhanced Risk (Level 3 of 5) for severe thunderstorms
across much Iowa on Friday. Damaging winds and tornadoes are the
primary threats. Large hail is also possible.

River flooding will also be possible this week as multiple rounds
of rainfall occur.

Freezing temperatures are expected in northern Iowa Friday night
and across much of the area Saturday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible later today.

Preliminary Local Storm Report
National Weather Service Des Moines IA
509 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0505 PM     Hail             3 E Des Moines Int Airp 41.53N 93.60W
04/15/2026  E0.88 Inch       Polk               IA   Trained Spotter

            Time estimated.

&&

Preliminary Local Storm Report
National Weather Service Des Moines IA
542 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0538 PM     Hail             3 W Chariton            41.02N 93.37W
04/15/2026  M1.00 Inch       Lucas              IA   Trained Spotter

            Largest hail was quarter sized.

&&

Fowle

Preliminary Local Storm Report
National Weather Service Des Moines IA
543 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0543 PM     Hail             Chariton                41.02N 93.31W
04/15/2026  E1.00 Inch       Lucas              IA   Trained Spotter

            Largest stones were quarter sized.

&&

Fowle

Preliminary Local Storm Report
National Weather Service Des Moines IA
548 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0543 PM     Hail             1 S Chariton            41.01N 93.31W
04/15/2026  E1.75 Inch       Lucas              IA   Trained Spotter

            Trained spotter reports hail of varying
            size, with the largest stones golf ball
            size.

&&

Preliminary Local Storm Report
National Weather Service Des Moines IA
557 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0545 PM     Hail             Chariton                41.02N 93.31W
04/15/2026  E2.00 Inch       Lucas              IA   Public

            Picture of 2 inch diameter hail shared by
            broadcast media.

&&

Fowle

Preliminary Local Storm Report
National Weather Service Des Moines IA
644 PM CDT Wed Apr 15 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0644 PM     Hail             5 ENE Millerton         40.86N 93.21W
04/15/2026  E0.88 Inch       Wayne              IA   Trained Spotter

&&

Fowle