Right now
The most recent data we hold from SPC arrived 9 hours ago, and this point is not in it. We record detections, not passes: an absence is not proof that nothing is there.
Nothing else has been detected within 20 km in the last 24 hours.
Reported by SPC 25 days ago.
It is the 7th strongest of the 108 detections recorded within 20 km of this point since 15 March 2026. Another comparable one was recorded here earlier the same day.
What the source measured
SPC reported: Wind UNK kt near 11 SW Alcester, Union, SD. EM report of semi blown off I-29 at approximately 9:21 pm between mile marker 33 and 34. Timing of damage aligns well with radar wind surge. (FSD)
Nearby, since 15 March 2026
- June 1, 2026 · 5.1 km
- September 4, 2026 · score 32 · 7.3 km
How we know
2 recorded sources include SPC; independence is not established by this count.
Our own score for this event is 16 out of 100.
This is our versioned heuristic index, not source severity or a calibrated probability. Urban PEI does not count unique people.
Computed under scoring rules v4. Rows carrying other versions were judged by different rules and are not directly comparable.
Event Data
| Type | Severe Weather |
| Severity | Medium |
| Calamity Score (ours) | 16 / 100 |
| Legacy data-support index | 0.61/1 |
| Coordinates | 42.9200, -96.8000 |
| Nearest City | Sioux City (57 km) |
| Urban exposure index (PEI) | 0 within 50 km |
| Impact Tier | minor |
| Timestamp | 2026-09-02T02:21:00.000Z |
| Source | https://www.spc.noaa.gov/climo/reports/today.html |
Physical priority index · v4 (historical). Heuristic priority, not calibrated probability, predictive accuracy or damage. The legacy data-support index combines assigned source support and field availability. Urban PEI is distance-weighted and does not count unique people; zero does not establish that nobody is present. Model cards.
Source and revision timeline
Source: spc. Occurrence: 2026-09-02T02:21:00.000Z.
First archived: 2026-09-02T06:40:51.133Z. Material modification: not recorded.
Retained revisions are prospective; earlier versions may be unavailable. No revision entry does not prove that a record never changed.
Score Breakdown
Technical Details
| ReportType | wind |
| Speed | UNK |
| Location | 11 SW Alcester |
| County | Union |
| State | SD |
| Comments | EM report of semi blown off I-29 at approximately 9:21 pm between mile marker 33 and 34. Timing of damage aligns well with radar wind surge. (FSD) |
| Iem TypeSummary | D |
| Iem City | 11 SW Alcester |
| Iem County | Union |
| Iem State | SD |
| Iem Wfo | FSD |
| Iem Remark | EM report of semi blown off I-29 at approximately 9:21 pm between mile marker 33 and 34. Timing of damage aligns well with radar wind surge. |
| MergedSources | [{"id":"iem_D_42.920_-96.800_1788315660000","source":"iem","severity":"low","severityValue":25,"timestamp":1788315660000,"latitude":42.92,"longitude":-96.8}] |
Safety Information
Always follow official guidance from your local emergency management agency. This platform provides scientific monitoring data and is not a substitute for official warnings. If you are in immediate danger, contact your local emergency number.
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.
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