This alert expired on 2 September 2026 at 03:30 UTC. It is kept here as a record.
No stronger detection stands among the 29 recorded within 20 km of this point since 15 March 2026 — one other scored the same. Another comparable one was recorded here earlier the same day.
What the source measured
NOAA reported: Tornado Warning issued September 1 at 10:18PM CDT until September 1 at 10:30PM CDT by NWS Sioux Falls SD
How we know
Confirmed by 3 independent sources, including NOAA.
Our own score for this event is 46 out of 100, at 71 % confidence.
The score is ours, computed from intensity, exposed population and local history — not the source’s.
Event Data
| Type | Severe weather |
| Severity | critical |
| Calamity Score (ours) | 46 / 100 |
| Our confidence | 71% |
| Coordinates | 43.2880, -95.9160 |
| Nearest City | Sioux Falls (71 km) |
| Impact Tier | minor |
| Timestamp | 2026-09-02T03:18:00.000Z |
| Source | https://api.weather.gov/alerts/urn%3Aoid%3A2.49.0.1.840.0.664d7e873a852787590c58c23a364d31f0658bc8.001.1 |
Score Breakdown
Technical Details
| Event | Tornado Warning |
| Urgency | Immediate |
| Certainty | Observed |
| AreaDesc | Lyon, IA; O'Brien, IA; Osceola, IA; Sioux, IA |
| Headline | Tornado Warning issued September 1 at 10:18PM CDT until September 1 at 10:30PM CDT by NWS Sioux Falls SD |
| Expires | 2026-09-01T22:30:00-05:00 |
| SenderName | NWS Sioux Falls SD |
| HasExactCoords | true |
| Spc ReportType | wind |
| Spc Speed | 81 |
| Spc Location | 9 NNE Hawarden |
| Spc County | Sioux |
| Spc State | IA |
| Spc Comments | Measured by personal weather station. (FSD) |
| Iem TypeSummary | H |
| Iem Magnitude | 0.7 |
| Iem Unit | Inch |
| Iem City | 3 SSE Lake Park |
| Iem County | Dickinson |
| Iem State | IA |
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 10 February 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 in this area?
Calamity.live data shows a weather event with CalamityScore 46/100 (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.