This alert is in force until 2 September 2026, 04:45 UTC.
It is the 4th strongest of the 337 detections recorded within 20 km of this point since 17 March 2026. Another comparable one was recorded here earlier the same day.
What the source measured
NOAA reported: Flash Flood Warning issued September 1 at 10:28PM EDT until September 2 at 12:45AM EDT by NWS Mount Holly NJ
An estimated 3,498,893 people live within 50 km of this point.
Nearby, since 17 March 2026
- July 27, 2026 · score 52 · 0.9 km
- July 28, 2026 · score 76 · 2.8 km
- July 21, 2026 · score 46 · 4.0 km
How we know
Confirmed by 4 independent sources, including NOAA.
Our own score for this event is 53 out of 100, at 91 % confidence.
The score is ours, computed from intensity, exposed population and local history — not the source’s.
Event Data
| Type | Severe weather |
| Severity | high |
| Calamity Score (ours) | 53 / 100 |
| Our confidence | 91% |
| Coordinates | 39.7906, -75.4170 |
| Nearest City | Chester (8 km) |
| Population Exposed | 3.5M within 50 km |
| Impact Tier | severe |
| Timestamp | 2026-09-02T02:28:00.000Z |
| Source | https://api.weather.gov/alerts/urn%3Aoid%3A2.49.0.1.840.0.4f0a7383ad561a8b8347ed60ee1c41720d8d3c8b.001.1 |
Score Breakdown
Technical Details
| Event | Flash Flood Warning |
| Urgency | Immediate |
| Certainty | Likely |
| AreaDesc | New Castle, DE; Gloucester, NJ; Salem, NJ; Chester, PA; Delaware, PA; Atlantic, NJ; Camden, NJ; Gloucester, NJ |
| Headline | Flash Flood Warning issued September 1 at 10:28PM EDT until September 2 at 12:45AM EDT by NWS Mount Holly NJ |
| Expires | 2026-09-02T00:45:00-04:00 |
| SenderName | NWS Mount Holly NJ |
| HasExactCoords | true |
| MergedCount | 2 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.4f0a7383ad561a8b8347ed60ee1c41720d8d3c8b.001.1","noaa_urn:oid:2.49.0.1.840.0.5ebe536de09e97831f4d52d9213353812270e84f.001.1"] |
| Spc ReportType | hail |
| Spc Speed | 100 |
| Spc Location | Williamstown |
| Spc County | Gloucester |
| Spc State | NJ |
| Spc Comments | Quarter size hail reported in Williamstown. (PHI) |
| Iem TypeSummary | G |
| Iem Magnitude | 53 |
| Iem Unit | MPH |
| Iem City | 1 S Odessa |
Safety Information
During flooding: never walk, swim, or drive through floodwaters. Six inches of moving water can knock you down, and one foot of water can sweep away a vehicle. Move to higher ground if waters rise. After flooding, avoid contact with floodwater which may contain sewage, chemicals, or debris. Follow local emergency service guidance.
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 near Chester?
Calamity.live data shows a weather event with CalamityScore 53/100, near Chester (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.