Alert archive / Virginia / Loudoun County / Severe Thunderstorm Warnings
Severe Thunderstorm Warnings in Loudoun County, Virginia, 2017
41 severe thunderstorm warnings in 2017. An alert counts here when it covered this county. The archive of severe thunderstorm warnings reaches back to 1986.
Loudoun County and its neighbors
Each county as a circle sized by its count in 2017. Tap one for its archive.
- Severe Thunderstorm Warnings
- 41
- Busiest month
- May7 severe thunderstorm warnings
- Busiest day
- June 19, 20176 severe thunderstorm warnings
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
33 of 41 severe thunderstorm warnings covering Loudoun County in 2017 had a qualifying storm report inside them; 27 of 35 hail, wind and damage reports fell inside a warning, on average 21 minutes after it went out.
Loudoun County, 2017
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Severe thunderstorm warnings | 41 | 33 | 20% | 35 | 77% | 21 min |
Each office's whole area, 2017
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Baltimore/Washington: severe thunderstorm warnings | 261 | 194 | 26% | 976 | 81% | 19 min |
An office's figures cover every county it serves, including across state lines.
Verified by the Iowa Environmental Mesonet's Cow, which matches each storm-based warning with the local storm reports inside its polygon while it was in force, within 15 km of its edge: a tornado warning counts as verified on a tornado report, a severe thunderstorm warning on hail of 1 inch or more, a gust of 58 mph or more, or wind damage, a flash flood warning on a flash flood report. The false alarm ratio is the share of warnings with no such report; "inside a warning" is the probability of detection, the share of reports that fell inside one; lead time runs from the warning's issue to each report inside it, counting zero for a report that came first. A warning with no report is not proof nothing happened: reports come from spotters, the public and damage surveys, and are thin where few people live.
The alerts
Every alert, in the order issued. Times are local, Eastern Time. Each opens its own page with the text, the map, the radar and the sounding.
| Issued | Product | Office | Lasted |
|---|---|---|---|
| Feb 12, 10:01 PM EST | Severe Thunderstorm Warning | LWX | 44 min |
| Feb 12, 10:29 PM EST | Severe Thunderstorm Warning | LWX | 61 min |
| Feb 12, 10:38 PM EST | Severe Thunderstorm Warning | LWX | 38 min |
| Feb 12, 11:02 PM EST | Severe Thunderstorm Warning | LWX | 43 min |
| Feb 25, 2:12 PM EST | Severe Thunderstorm Warning | LWX | 10 min |
| Mar 1, 12:26 PM EST | Severe Thunderstorm Warning | LWX | 49 min |
| Mar 1, 12:42 PM EST | Severe Thunderstorm Warning | LWX | 48 min |
| Mar 1, 1:05 PM EST | Severe Thunderstorm Warning | LWX | 40 min |
| Mar 1, 1:14 PM EST | Severe Thunderstorm Warning | LWX | 46 min |
| Apr 6, 1:12 PM EDT | Severe Thunderstorm Warning | LWX | 48 min |
| Apr 21, 4:00 PM EDT | Severe Thunderstorm Warning | LWX | 45 min |
| Apr 30, 2:39 PM EDT | Severe Thunderstorm Warning | LWX | 37 min |
| May 18, 6:00 PM EDT | Severe Thunderstorm Warning | LWX | 24 min |
| May 18, 6:27 PM EDT | Severe Thunderstorm Warning | LWX | 63 min |
| May 18, 7:03 PM EDT | Severe Thunderstorm Warning | LWX | 42 min |
| May 18, 7:24 PM EDT | Severe Thunderstorm Warning | LWX | 66 min |
| May 18, 7:39 PM EDT | Severe Thunderstorm Warning | LWX | 66 min |
| May 30, 6:15 PM EDT | Severe Thunderstorm Warning | LWX | 22 min |
| May 31, 5:12 PM EDT | Severe Thunderstorm Warning | LWX | 26 min |
| Jun 19, 12:59 PM EDT | Severe Thunderstorm Warning | LWX | 46 min |
| Jun 19, 2:00 PM EDT | Severe Thunderstorm Warning | LWX | 25 min |
| Jun 19, 2:07 PM EDT | Severe Thunderstorm Warning | LWX | 38 min |
| Jun 19, 2:45 PM EDT | Severe Thunderstorm Warning | LWX | 45 min |
| Jun 19, 3:00 PM EDT | Severe Thunderstorm Warning | LWX | 45 min |
| Jun 19, 3:19 PM EDT | Severe Thunderstorm Warning | LWX | 41 min |
| Jul 1, 2:38 PM EDT | Severe Thunderstorm Warning | LWX | 41 min |
| Jul 7, 7:40 PM EDT | Severe Thunderstorm Warning | LWX | 35 min |
| Jul 11, 5:41 PM EDT | Severe Thunderstorm Warning | LWX | 49 min |
| Jul 14, 3:24 PM EDT | Severe Thunderstorm Warning | LWX | 39 min |
| Jul 14, 4:14 PM EDT | Severe Thunderstorm Warning | LWX | 27 min |
| Jul 22, 12:57 PM EDT | Severe Thunderstorm Warning | LWX | 48 min |
| Aug 3, 5:55 PM EDT | Severe Thunderstorm Warning | LWX | 35 min |
| Aug 3, 6:47 PM EDT | Severe Thunderstorm Warning | LWX | 24 min |
| Aug 3, 8:11 PM EDT | Severe Thunderstorm Warning | LWX | 26 min |
| Aug 4, 9:49 PM EDT | Severe Thunderstorm Warning | LWX | 41 min |
| Aug 12, 5:58 PM EDT | Severe Thunderstorm Warning | LWX | 47 min |
| Aug 12, 6:30 PM EDT | Severe Thunderstorm Warning | LWX | 17 min |
| Sep 5, 3:51 PM EDT | Severe Thunderstorm Warning | LWX | 39 min |
| Sep 5, 4:16 PM EDT | Severe Thunderstorm Warning | LWX | 29 min |
| Sep 5, 4:46 PM EDT | Severe Thunderstorm Warning | LWX | 44 min |
| Sep 5, 5:34 PM EDT | Severe Thunderstorm Warning | LWX | 26 min |
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordForecastThe radar archive20162018
Sources
National Weather Service watches, warnings, advisories and statements from the Iowa Environmental Mesonet's VTEC archive, which reconstructs tornado, severe thunderstorm, flash flood and marine warnings back to 1986 from the NWS text archive. Storm Prediction Center watches and mesoscale discussions from SPC's archive through the Mesonet. County centers from the US Census Bureau. Warning verification from the Mesonet's Cow. Rebuilt daily.