Right now
The most recent data we hold from NOAA arrived 69 minutes 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.
This alert expired on 18 May 2026 at 23:45 UTC. It is kept here as a record.
It is the 10th strongest of the 46 detections recorded within 20 km of this point since 16 March 2026. Another comparable one was recorded here earlier the same day. 9 more were recorded here in the fortnight before it.
What the source measured
NOAA reported: Severe Thunderstorm Warning issued May 18 at 6:29PM CDT until May 18 at 6:45PM CDT by NWS Sioux Falls SD
Urban PEI: 82,821 within a heuristic 50 km radius; not unique people.
Nearby, since 16 March 2026
- May 17, 2026 · score 39 · 14.4 km
- September 4, 2026 · score 32 · 16.7 km
- June 1, 2026 · score 46 · 18.3 km
How we know
13 recorded sources include NOAA; independence is not established by this count.
Our own score for this event is 39 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 v1. Rows carrying other versions were judged by different rules and are not directly comparable.
Event Data
| Type | Severe Weather |
| Severity | Medium |
| Calamity Score (ours) | 39 / 100 |
| Legacy data-support index | 0.90/1 |
| Coordinates | 42.8129, -96.5529 |
| Nearest City | Sioux City (37 km) |
| Urban exposure index (PEI) | 82.8K within 50 km |
| Impact Tier | significant |
| Timestamp | 2026-05-18T23:29:00.000Z |
| Source | https://api.weather.gov/alerts/urn:oid:2.49.0.1.840.0.0cf1b889e2cafd18936c3de187ce7dbff6106695.002.1 |
Physical priority index · v1. 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: noaa. Occurrence: 2026-05-18T23:29:00.000Z.
First archived: 2026-05-18T23:43:10.746Z. 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
| Event | Severe Thunderstorm Warning |
| Urgency | Immediate |
| Certainty | Observed |
| AreaDesc | Plymouth, IA; Sioux, IA; Union, SD |
| Headline | Severe Thunderstorm Warning issued May 18 at 6:29PM CDT until May 18 at 6:45PM CDT by NWS Sioux Falls SD |
| Expires | 2026-05-18T18:45:00-05:00 |
| SenderName | NWS Sioux Falls SD |
| HasExactCoords | true |
| Iem TypeSummary | H |
| Iem Magnitude | 0.88 |
| Iem Unit | Inch |
| Iem City | 2 N Sioux City |
| Iem County | Woodbury |
| Iem State | IA |
| Iem Wfo | FSD |
| MergedSources | [{"id":"iem_H_42.410_-96.840_1779145320000","source":"iem","severity":"low","severityValue":25,"timestamp":1779145320000,"latitude":42.41,"longitude":-96.84},{"id":"iem_H_42.260_-96.940_1779144720000","source":"iem","severity":"low","severityValue":25,"timestamp":1779144720000,"latitude":42.26,"longitude":-96.94},{"id":"iem_H_42.390_-96.030_1779142380000","source":"iem","severity":"low","severityValue":25,"timestamp":1779142380000,"latitude":42.39,"longitude":-96.03},{"id":"iem_H_42.480_-95.780_1779143160000","source":"iem","severity":"low","severityValue":25,"timestamp":1779143160000,"latitude":42.48,"longitude":-95.78},{"id":"iem_H_42.380_-96.990_1779139080000","source":"iem","severity":"low","severityValue":25,"timestamp":1779139080000,"latitude":42.38,"longitude":-96.99},{"id":"iem_H_42.460_-95.840_1779142980000","source":"iem","severity":"low","severityValue":25,"timestamp":1779142980000,"latitude":42.46,"longitude":-95.84},{"id":"iem_H_42.530_-96.770_1779145800000","source":"iem","severity":"low","severityValue":25,"timestamp":1779145800000,"latitude":42.53,"longitude":-96.77},{"id":"iem_H_42.580_-95.720_1779143700000","source":"iem","severity":"low","severityValue":25,"timestamp":1779143700000,"latitude":42.58,"longitude":-95.72},{"id":"iem_H_42.830_-96.560_1779141000000","source":"iem","severity":"low","severityValue":25,"timestamp":1779141000000,"latitude":42.83,"longitude":-96.56},{"id":"iem_H_42.230_-97.000_1779144600000","source":"iem","severity":"low","severityValue":25,"timestamp":1779144600000,"latitude":42.23,"longitude":-97},{"id":"iem_H_42.600_-95.710_1779143940000","source":"iem","severity":"low","severityValue":25,"timestamp":1779143940000,"latitude":42.6,"longitude":-95.71},{"id":"iem_H_42.530_-96.390_1779141720000","source":"iem","severity":"low","severityValue":25,"timestamp":1779141720000,"latitude":42.53,"longitude":-96.39}] |
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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