This alert expired on 20 May 2026 at 20:00 UTC. It is kept here as a record.
It is the 26th strongest of the 101 detections recorded within 20 km of this point since 12 March 2026. Another comparable one was recorded here earlier the same day. 6 more were recorded here in the fortnight before it.
What the source measured
NOAA reported: Severe Thunderstorm Warning issued May 20 at 3:24PM EDT until May 20 at 4:00PM EDT by NWS Baltimore MD/Washington DC
An estimated 631,794 people live within 50 km of this point.
Nearby, since 12 March 2026
- August 10, 2026 · score 48 · 7.9 km
- July 21, 2026 · score 41 · 8.5 km
- August 10, 2026 · score 43 · 10.7 km
How we know
Confirmed by 4 independent sources, including NOAA.
Our own score for this event is 48 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 | medium |
| Calamity Score (ours) | 48 / 100 |
| Our confidence | 91% |
| Coordinates | 39.1803, -77.7996 |
| Nearest City | Leesburg (22 km) |
| Population Exposed | 631.8K within 50 km |
| Impact Tier | significant |
| Date | 2026-05-20 — time not reported by the source |
| Source | https://api.weather.gov/alerts/merged_Severe Thunderstorm Warning_noaa_urn:oid:2.49.0.1.840.0.bd26181b2c0736ba4cbc43272ec8d47c |
Score Breakdown
Technical Details
| Event | Severe Thunderstorm Warning |
| Urgency | Immediate |
| Certainty | Observed |
| AreaDesc | Clarke, VA; Frederick, VA; Warren, VA; Loudoun, VA; Frederick, MD; Washington, MD; Loudoun, VA; Jefferson, WV |
| Headline | Severe Thunderstorm Warning issued May 20 at 3:24PM EDT until May 20 at 4:00PM EDT by NWS Baltimore MD/Washington DC |
| Expires | 2026-05-20T16:00:00-04:00 |
| SenderName | NWS Baltimore MD/Washington DC |
| HasExactCoords | true |
| MergedCount | 3 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.bd26181b2c0736ba4cbc43272ec8d47ccce4bbca.001.1","noaa_urn:oid:2.49.0.1.840.0.d8b5a2aaf5c67c4bac7271b6a01cd6c55b6ea231.001.1","noaa_urn:oid:2.49.0.1.840.0.c83f1acf2d76de3614bce406b95f08d274f4e530.001.1"] |
| Iem TypeSummary | D |
| Iem City | 4 WNW Greencastle |
| Iem County | Franklin |
| Iem State | PA |
| Iem Wfo | CTP |
| Iem Remark | Wires down reported in Upton along Lemar Road and Buchanan Trail West. |
| Google News RssFeed | weather |
| Google News SourceName | The Washington Post |
| MergedSources | [{"id":"iem_D_39.760_-77.860_1779298500000","source":"iem","severity":"low","severityValue":25,"timestamp":1779298500000,"latitude":39.76,"longitude":-77.86},{"id":"iem_D_39.810_-77.810_1779298980000","source":"iem","severity":"low","severityValue":25,"timestamp":1779298980000,"latitude":39.81,"longitude":-77.81},{"id":"gnews_weather_494250_192","source":"google_news","severity":"medium","severityValue":40,"timestamp":1779302743000,"latitude":38.9,"longitude":-77.04}] |
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 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.
Calamity.live data shows a weather event with CalamityScore 48/100, near Leesburg (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 188 scientific monitoring sources.