Right now
The most recent data we hold from NOAA arrived 6 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 21 July 2026 at 21:15 UTC. It is kept here as a record.
It is the 88th strongest of the 184 detections recorded within 20 km of this point since 11 March 2026. The last comparable one was on 18 July 2026. 3 more were recorded here in the fortnight before it.
What the source measured
NOAA reported: Severe Thunderstorm Warning issued July 21 at 4:23PM EDT until July 21 at 5:15PM EDT by NWS Mount Holly NJ
Urban PEI: 1,893,453 within a heuristic 50 km radius; not unique people.
Nearby, since 11 March 2026
- July 21, 2026 · score 46 · 2.7 km
- March 16, 2026 · score 52 · 4.8 km
- August 8, 2026 · score 46 · 5.2 km
How we know
One source: NOAA. Not yet confirmed by a second, independent source.
Our own score for this event is 46 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) | 46 / 100 |
| Legacy data-support index | 0.79/1 |
| Coordinates | 39.2757, -76.1811 |
| Nearest City | Edgewood (19 km) |
| Urban exposure index (PEI) | 1.9M within 50 km |
| Impact Tier | significant |
| Timestamp | 2026-07-21T20:27:00.000Z |
| Source | https://api.weather.gov/alerts/merged_Severe Thunderstorm Warning_noaa_urn:oid:2.49.0.1.840.0.6c24dc889894de7afee86951fbe3dbd3 |
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: 2026-07-21T20:27:00.000Z.
First archived: 2026-07-21T20:35:59.199Z. 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 | Chester, PA; Delaware, PA; Montgomery, PA; Philadelphia, PA; New Castle, DE; Chester, PA; Delaware, PA; Charles, MD; Prince Georges, MD and 5 more areas |
| Headline | Severe Thunderstorm Warning issued July 21 at 4:23PM EDT until July 21 at 5:15PM EDT by NWS Mount Holly NJ |
| Expires | 2026-07-21T17:15:00-04:00 |
| SenderName | NWS Mount Holly NJ |
| HasExactCoords | true |
| MergedCount | 8 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.6c24dc889894de7afee86951fbe3dbd3618195bd.001.1","noaa_urn:oid:2.49.0.1.840.0.9865d103731a858b9fb94398b7c8b6bb45a72ea3.001.1","noaa_urn:oid:2.49.0.1.840.0.a496c7d6821e4affb467f50f6ed8956ef7fa6291.001.1","noaa_urn:oid:2.49.0.1.840.0.73e1c86203107f7854c32759b0140cf61f5288f4.001.1","noaa_urn:oid:2.49.0.1.840.0.64a58cb04851c97436a8ad826247830746c9c7ed.001.1","noaa_urn:oid:2.49.0.1.840.0.9c8537af120e6b0682cc050197b8ef0dff4fbd7f.001.1","noaa_urn:oid:2.49.0.1.840.0.a3d11dfaee8d4ac7c1cf0685301e8eaf60053ee2.001.1","noaa_urn:oid:2.49.0.1.840.0.a2824d2f61ecab06edb5dfe4ce6770d0c940f36d.001.1"] |
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.
Review the area, threshold and delivery channel in your account.
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