Alert archive / Iowa / Mesoscale Discussions in 2026

Mesoscale Discussion 765

May 17, 20264 states

The Storm Prediction Center issued this mesoscale discussion at May 17, 2026, 9:30 PM CDT for 4 states. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued
May 17, 2026, 9:30 PM CDT (02:30 UTC)
Expired
May 17, 2026, 11:00 PM CDT
In force
90 min
Issued by
the Storm Prediction Center
Concerning
Tornado watch 216...218
All 58 counties

Adair County, IA, Adams County, IA, Audubon County, IA, Boone County, IA, Butler County, IA, Calhoun County, IA, Carroll County, IA, Cass County, IA, Cerro Gordo County, IA, Clarke County, IA, Dallas County, IA, Decatur County, IA, Floyd County, IA, Franklin County, IA, Fremont County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hancock County, IA, Hardin County, IA, Humboldt County, IA, Jasper County, IA, Kossuth County, IA, Lucas County, IA, Madison County, IA, Marion County, IA, Marshall County, IA, Mills County, IA, Mitchell County, IA, Montgomery County, IA, Page County, IA, Polk County, IA, Ringgold County, IA, Story County, IA, Taylor County, IA, Union County, IA, Warren County, IA, Wayne County, IA, Webster County, IA, Winnebago County, IA, Worth County, IA, Wright County, IA, Faribault County, MN, Freeborn County, MN, Mower County, MN, Steele County, MN, Waseca County, MN, Andrew County, MO, Atchison County, MO, Gentry County, MO, Harrison County, MO, Holt County, MO, Mercer County, MO, Nodaway County, MO, Worth County, MO, Nemaha County, NE, Richardson County, NE

The radar

The Des Moines radar (KDMX), 36 km from the middle of the area, began a volume at 02:30 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 2.5 hours before the alert went out and 208 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2026-05-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2478 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Omaha, NE at 00:00Z on 2026-05-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 178 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
2478 J/kg
Mixed-layer CIN
-15 J/kg
Mixed-layer LCL
1258 m above ground
0-6 km bulk shear
34 kt
0-1 km storm-relative helicity
178 m²/s²
0-3 km storm-relative helicity
298 m²/s²
Significant tornado parameter
2.0
Supercell composite
17.9

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 17, 7:40 PM CDTMesoscale DiscussionSPCAdair, Adams, Audubon, Boone, Calhoun, Carroll and 29 more65 min
May 17, 7:49 PM CDTMesoscale DiscussionSPCCerro Gordo, Emmet, Floyd, Franklin, Hancock, Howard and 7 more56 min
May 17, 8:07 PM CDTTornado WatchSPCAdair, Adams, Audubon, Black Hawk, Boone, Calhoun and 29 more5 hr
May 17, 8:18 PM CDTMesoscale DiscussionSPCBuena Vista, Cherokee, Clay, Emmet, Humboldt, Ida and 5 more27 min
May 17, 10:32 PM CDTMesoscale DiscussionSPCAllamakee, Black Hawk, Boone, Bremer, Buchanan, Butler and 14 more118 min
May 17, 11:10 PM CDTSevere Thunderstorm WatchSPCAllamakee, Appanoose, Benton, Buchanan, Cedar, Clayton and 13 more5 hr
May 18, 1:24 AM CDTMesoscale DiscussionSPCAppanoose, Cedar, Davis, Dubuque, Henry, Iowa and 12 more96 min
May 18, 6:51 AM CDTMesoscale DiscussionSPCDes Moines, Henry, Lee84 min
May 18, 3:29 PM CDTMesoscale DiscussionSPCAdair, Adams, Audubon, Cass, Clarke, Decatur and 12 more2 hr
May 18, 3:49 PM CDTTornado WatchSPCAdair, Adams, Appanoose, Cass, Clarke, Davis and 21 more6 hr
May 18, 5:10 PM CDTMesoscale DiscussionSPCCherokee, Lyon, Monona, O'Brien, Osceola, Plymouth and 2 more95 min
May 18, 11:59 AM CDTMesoscale DiscussionSPCHolt2 hr
May 18, 5:45 PM CDTMesoscale DiscussionSPCAndrew, Atchison, Holt, Nodaway2 hr
May 18, 6:14 PM CDTTornado WatchSPCAdair, Bates, Caldwell, Carroll, Cass, Chariton and 19 more7 hr
May 18, 12:50 PM CDTTornado Watch PDSSPCGage, Jefferson, Johnson, Nemaha, Otoe, Pawnee and 1 more7 hr

Nearby

Mesoscale Discussions in Iowa, 2026Mesoscale Discussions in Missouri, 2026Mesoscale Discussions in Minnesota, 2026Every mesoscale discussion in 2026

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.