This alert expired on 18 May 2026 at 06:00 UTC. It is kept here as a record.
It is the 7th strongest of the 243 detections recorded within 20 km of this point since 10 March 2026. Another comparable one was recorded here earlier the same day. 37 more were recorded here in the fortnight before it.
What the source measured
NOAA reported: Tornado Watch issued May 17 at 11:47PM CDT until May 18 at 1:00AM CDT by NWS La Crosse WI
An estimated 181,553 people live within 50 km of this point.
Nearby, since 10 March 2026
- September 2, 2026 · score 37 · 0.0 km
- September 1, 2026 · score 37 · 0.0 km
- August 13, 2026 · score 43 · 0.0 km
How we know
One source: NOAA. Not yet confirmed by a second, independent source.
Our own score for this event is 55 out of 100, at 80 % confidence.
The score is ours, computed from intensity, exposed population and local history — not the source’s.
Computed under scoring rules v1. Rows carrying other versions were judged by different rules and are not directly comparable.
Event Data
| Type | Severe Weather |
| Severity | High |
| Calamity Score (ours) | 55 / 100 |
| Our confidence | 80% |
| Coordinates | 42.0000, -93.2000 |
| Nearest City | Marshalltown (25 km) |
| Population Exposed | 181.6K within 50 km |
| Impact Tier | severe |
| Timestamp | 2026-05-18T04:47:00.000Z |
| Source | https://api.weather.gov/alerts/merged_Tornado Watch_noaa_urn:oid:2.49.0.1.840.0.3b50e892e6f23a259c3344d0dc555aec |
Score Breakdown
Technical Details
| Event | Tornado Watch |
| Urgency | Future |
| Certainty | Possible |
| AreaDesc | Chickasaw, IA; Fayette, IA; Howard, IA; Winneshiek, IA; Fillmore, MN; Olmsted, MN; Black Hawk, IA; Clarke, IA; Decatur, IA; Grundy, IA; Jasper, IA; Lucas, IA; Madison, IA; Mahaska, IA; Marion, IA; Marshall, IA; Monroe, IA; Polk, IA; Poweshiek, IA; Ringgold, IA; Tama, IA; Taylor, IA; Union, IA; Warren, IA; Wayne, IA; Bremer, IA; Butler, IA |
| Headline | Tornado Watch issued May 17 at 11:47PM CDT until May 18 at 1:00AM CDT by NWS La Crosse WI |
| Expires | 2026-05-18T01:00:00-05:00 |
| SenderName | NWS La Crosse WI |
| HasExactCoords | false |
| MergedCount | 3 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.3b50e892e6f23a259c3344d0dc555aec5eee7501.002.1","noaa_urn:oid:2.49.0.1.840.0.3685800154afba0204bc9472382b8a7d4abcf833.002.1","noaa_urn:oid:2.49.0.1.840.0.3685800154afba0204bc9472382b8a7d4abcf833.003.1"] |
Safety Information
If a tornado warning is issued: go to a basement or an interior room on the lowest floor, away from windows. A vehicle and a mobile home are not shelter. Cover your head and neck. Wait for the official all-clear before going outside, and watch for downed power lines and gas leaks afterwards.
Series begins 8 March 2026. Comparisons refer to that period only. Collection gap: 14-26 August 2026.
This data is aggregated algorithmically from scientific sources. Not a replacement for official emergency warnings.
Want to know when something happens near Marshalltown?
Calamity.live data shows a weather event with CalamityScore 55/100, near Marshalltown (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.