This alert expired on 20 May 2026 at 20:15 UTC. It is kept here as a record.
It is the 69th strongest of the 104 detections recorded within 20 km of this point since 12 March 2026. Another comparable one was recorded here earlier the same day. 5 more were recorded here in the fortnight before it.
What the source measured
NOAA reported: Severe Thunderstorm Warning issued May 20 at 3:52PM EDT until May 20 at 4:15PM EDT by NWS Baltimore MD/Washington DC
An estimated 611,250 people live within 50 km of this point.
Nearby, since 12 March 2026
- August 7, 2026 · score 37 · 2.0 km
- March 12, 2026 · score 52 · 7.4 km
- March 17, 2026 · score 52 · 12.8 km
How we know
Confirmed by 5 independent sources, including NOAA.
Our own score for this event is 48 out of 100, at 90 % 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 | 90% |
| Coordinates | 39.6070, -77.1813 |
| Nearest City | Westminster (16 km) |
| Population Exposed | 611.3K within 50 km |
| Impact Tier | significant |
| Timestamp | 2026-05-20T19:52:00.000Z |
| Source | https://api.weather.gov/alerts/merged_Severe Thunderstorm Warning_noaa_urn:oid:2.49.0.1.840.0.0ffe476efd628c87f990033aee2183a1 |
Score Breakdown
Technical Details
| Event | Severe Thunderstorm Warning |
| Urgency | Immediate |
| Certainty | Observed |
| AreaDesc | Carroll, MD; Frederick, MD; Lancaster, PA; York, PA; Clarke, VA; Frederick, VA; Warren, VA and 2 more areas |
| Headline | Severe Thunderstorm Warning issued May 20 at 3:52PM EDT until May 20 at 4:15PM EDT by NWS Baltimore MD/Washington DC |
| Expires | 2026-05-20T16:15:00-04:00 |
| SenderName | NWS Baltimore MD/Washington DC |
| HasExactCoords | true |
| MergedCount | 5 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.0ffe476efd628c87f990033aee2183a186286278.001.1","noaa_urn:oid:2.49.0.1.840.0.5ed1aff7c835f2ae9a3254701b57db7e124869e0.001.1","noaa_urn:oid:2.49.0.1.840.0.798014344386f4557f5494e7a0adcd23d2fe21b7.001.1","noaa_urn:oid:2.49.0.1.840.0.b6dd6edc202b43936fad86731e9dae1a2ed34101.001.1","noaa_urn:oid:2.49.0.1.840.0.55ce805d4e6d30164e3c1dbd85356d0d8e94943e.001.1"] |
| Iem TypeSummary | D |
| Iem City | 3 SSE Round Hill |
| Iem County | Loudoun |
| Iem State | VA |
| Iem Wfo | LWX |
| Iem Remark | Trees blew down on Paxson Road just west of VA-690 Silcott Springs Road. |
| 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_39.340_-77.510_1779304260000","source":"iem","severity":"low","severityValue":25,"timestamp":1779304260000,"latitude":39.34,"longitude":-77.51},{"id":"iem_D_39.810_-77.810_1779298980000","source":"iem","severity":"low","severityValue":25,"timestamp":1779298980000,"latitude":39.81,"longitude":-77.81},{"id":"iem_D_39.100_-77.740_1779303720000","source":"iem","severity":"low","severityValue":25,"timestamp":1779303720000,"latitude":39.1,"longitude":-77.74}] |
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 Westminster (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 188 scientific monitoring sources.