Alert archive / Virginia / Loudoun County
Weather alerts in Loudoun County, Virginia, 2017
135 weather alerts in 2017, from the National Weather Service and the Storm Prediction Center. An alert counts here when it covered this county.
Loudoun County and its neighbors
Each county as a circle sized by its count in 2017. Tap one for its archive.
- Alerts
- 135
- Warnings
- 50
- Watches
- 18
- Advisories
- 32
- Busiest month
- July21 alerts
- Busiest day
- June 19, 20179 alerts
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
1 of 1 tornado warnings covering Loudoun County in 2017 had a tornado report inside them.
Loudoun County, 2017
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Tornado warnings | 1 | 1 | 0% | 0 | ||
| Severe thunderstorm warnings | 41 | 33 | 20% | 35 | 77% | 21 min |
| Flash flood warnings | 2 | 1 | 50% | 2 | 100% | 86 min |
Each office's whole area, 2017
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Baltimore/Washington: tornado warnings | 11 | 4 | 64% | 18 | 33% | 7 min |
| NWS Baltimore/Washington: severe thunderstorm warnings | 261 | 194 | 26% | 976 | 81% | 19 min |
| NWS Baltimore/Washington: flash flood warnings | 49 | 34 | 31% | 130 | 81% | 78 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 |
|---|---|---|---|
| Jan 4, 8:13 PM EST | Winter Weather Advisory | LWX | 32 hr |
| Jan 10, 7:16 AM EST | Special Weather Statement | LWX | 89 min |
| Jan 10, 8:50 AM EST | Special Weather Statement | LWX | 55 min |
| Jan 10, 9:06 AM EST | Winter Weather Advisory | LWX | 2 hr |
| Jan 10, 1:32 PM EST | Freezing Rain Advisory | LWX | 14 hr |
| Jan 13, 3:32 AM EST | Winter Weather Advisory | LWX | 47 hr |
| Jan 17, 9:20 PM EST | Dense Fog Advisory | LWX | 7 hr |
| Jan 21, 12:06 AM EST | Dense Fog Advisory | LWX | 13 hr |
| Jan 21, 8:42 PM EST | Dense Fog Advisory | LWX | 14 hr |
| Jan 22, 1:51 PM EST | Wind Advisory | LWX | 26 hr |
| Jan 26, 3:35 AM EST | Wind Advisory | LWX | 15 hr |
| Feb 8, 10:17 AM EST | Winter Weather Advisory | LWX | 21 hr |
| Feb 9, 8:57 AM EST | Wind Advisory | LWX | 9 hr |
| Feb 11, 2:22 PM EST | High Wind Watch | LWX | 13 hr |
| Feb 12, 3:36 AM EST | High Wind Warning | LWX | 32 hr |
| Feb 12, 3:36 AM EST | Wind Advisory | LWX | 37 hr |
| Feb 12, 9:49 PM EST | Special Weather Statement | LWX | 116 min |
| 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, 12:24 PM EST | Mesoscale Discussion | SPC | 2 hr |
| Feb 25, 1:30 PM EST | Severe Thunderstorm Watch | SPC | 6 hr |
| Feb 25, 2:12 PM EST | Severe Thunderstorm Warning | LWX | 10 min |
| Mar 1, 9:44 AM EST | Mesoscale Discussion | SPC | 91 min |
| Mar 1, 10:38 AM EST | Severe Thunderstorm Watch | SPC | 4 hr |
| Mar 1, 12:25 PM EST | Mesoscale Discussion | SPC | 65 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 |
| Mar 1, 2:47 PM EST | Wind Advisory | LWX | 18 hr |
| Mar 11, 7:52 PM EST | Winter Storm Watch | LWX | 31 hr |
| Mar 12, 2:58 PM EDT | Winter Storm Warning | LWX | 47 hr |
| Mar 13, 4:00 AM EDT | Winter Weather Advisory | LWX | 34 hr |
| Mar 13, 10:01 PM EDT | Mesoscale Discussion | SPC | 4 hr |
| Mar 14, 3:22 AM EDT | Mesoscale Discussion | SPC | 5 hr |
| Mar 15, 3:52 AM EDT | Wind Advisory | LWX | 16 hr |
| Mar 21, 10:00 AM EDT | Special Weather Statement | LWX | 15 min |
| Mar 27, 4:37 AM EDT | Dense Fog Advisory | LWX | 5 hr |
| Apr 6, 12:45 PM EDT | Severe Thunderstorm Watch | SPC | 4 hr |
| Apr 6, 1:12 PM EDT | Severe Thunderstorm Warning | LWX | 48 min |
| Apr 6, 1:26 PM EDT | Tornado Warning | LWX | 19 min |
| Apr 6, 4:24 PM EDT | Freeze Watch | LWX | 21 hr |
| Apr 7, 1:31 PM EDT | Freeze Warning | LWX | 19 hr |
| Apr 8, 2:10 PM EDT | Frost Advisory | LWX | 18 hr |
| Apr 21, 4:00 PM EDT | Severe Thunderstorm Warning | LWX | 45 min |
| Apr 21, 4:19 PM EDT | Mesoscale Discussion | SPC | 56 min |
| Apr 30, 2:39 PM EDT | Severe Thunderstorm Warning | LWX | 37 min |
| Apr 30, 3:25 PM EDT | Mesoscale Discussion | SPC | 95 min |
| May 1, 5:54 PM EDT | Severe Thunderstorm Watch | SPC | 5 hr |
| May 1, 8:28 PM EDT | Mesoscale Discussion | SPC | 92 min |
| May 5, 6:15 PM EDT | Mesoscale Discussion | SPC | 90 min |
| May 8, 12:41 PM EDT | Frost Advisory | LWX | 19 hr |
| 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, 6:50 PM EDT | Flash Flood Warning | LWX | 3 hr |
| 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 19, 3:36 PM EDT | Mesoscale Discussion | SPC | 114 min |
| May 25, 12:59 PM EDT | Mesoscale Discussion | SPC | 61 min |
| May 28, 1:42 AM EDT | Dense Fog Advisory | LWX | 6 hr |
| May 30, 5:56 PM EDT | Mesoscale Discussion | SPC | 64 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, 4:09 AM EDT | Flash Flood Watch | LWX | 14 hr |
| Jun 19, 12:14 PM EDT | Mesoscale Discussion | SPC | 2 hr |
| Jun 19, 12:48 PM EDT | Severe Thunderstorm Watch | SPC | 8 hr |
| 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 |
| Jun 21, 2:38 PM EDT | Mesoscale Discussion | SPC | 3 hr |
| Jun 23, 8:25 PM EDT | Mesoscale Discussion | SPC | 65 min |
| Jul 1, 12:54 PM EDT | Mesoscale Discussion | SPC | 66 min |
| Jul 1, 1:34 PM EDT | Severe Thunderstorm Watch | SPC | 7 hr |
| Jul 1, 2:38 PM EDT | Severe Thunderstorm Warning | LWX | 41 min |
| Jul 6, 6:20 AM EDT | Flash Flood Watch | LWX | 20 hr |
| 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, 1:09 PM EDT | Mesoscale Discussion | SPC | 2 hr |
| Jul 14, 1:40 PM EDT | Severe Thunderstorm Watch | SPC | 7 hr |
| 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 14, 4:23 PM EDT | Mesoscale Discussion | SPC | 67 min |
| Jul 18, 2:31 PM EDT | Mesoscale Discussion | SPC | 59 min |
| Jul 20, 3:21 AM EDT | Heat Advisory | LWX | 16 hr |
| Jul 20, 8:30 PM EDT | Heat Advisory | LWX | 23 hr |
| Jul 22, 12:57 PM EDT | Severe Thunderstorm Warning | LWX | 48 min |
| Jul 22, 1:12 PM EDT | Mesoscale Discussion | SPC | 3 hr |
| Jul 24, 2:17 PM EDT | Mesoscale Discussion | SPC | 118 min |
| Jul 24, 6:09 PM EDT | Mesoscale Discussion | SPC | 3 hr |
| Jul 27, 1:47 PM EDT | Flash Flood Watch | LWX | 48 hr |
| Jul 28, 10:51 PM EDT | Flash Flood Warning | LWX | 4 hr |
| Jul 29, 8:40 AM EDT | Areal Flood Warning | LWX | 6 hr |
| Aug 2, 1:30 PM EDT | Mesoscale Discussion | SPC | 2 hr |
| Aug 3, 5:55 PM EDT | Severe Thunderstorm Warning | LWX | 35 min |
| Aug 3, 6:28 PM EDT | Mesoscale Discussion | SPC | 62 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 11, 3:48 PM EDT | Mesoscale Discussion | SPC | 87 min |
| Aug 12, 4:11 PM EDT | Severe Thunderstorm Watch | SPC | 7 hr |
| Aug 12, 5:58 PM EDT | Severe Thunderstorm Warning | LWX | 47 min |
| Aug 12, 6:30 PM EDT | Severe Thunderstorm Warning | LWX | 17 min |
| Aug 15, 10:31 PM EDT | Dense Fog Advisory | LWX | 11 hr |
| Aug 18, 12:35 PM EDT | Flash Flood Watch | LWX | 8 hr |
| Aug 18, 1:54 PM EDT | Mesoscale Discussion | SPC | 2 hr |
| Aug 18, 2:27 PM EDT | Severe Thunderstorm Watch | SPC | 9 hr |
| Aug 18, 4:34 PM EDT | Mesoscale Discussion | SPC | 86 min |
| Aug 19, 8:16 PM EDT | Mesoscale Discussion | SPC | 59 min |
| Aug 21, 2:53 PM EDT | Mesoscale Discussion | SPC | 2 hr |
| Sep 5, 2:31 PM EDT | Mesoscale Discussion | SPC | 59 min |
| Sep 5, 3:26 PM EDT | Severe Thunderstorm Watch | SPC | 5 hr |
| 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, 5:00 PM EDT | Mesoscale Discussion | SPC | 90 min |
| Sep 5, 5:34 PM EDT | Severe Thunderstorm Warning | LWX | 26 min |
| Oct 16, 12:30 PM EDT | Frost Advisory | LWX | 20 hr |
| Oct 17, 1:39 PM EDT | Frost Advisory | LWX | 19 hr |
| Oct 23, 6:31 PM EDT | Wind Advisory | LWX | 10 hr |
| Oct 26, 3:53 AM EDT | Frost Advisory | LWX | 29 hr |
| Oct 29, 3:44 AM EDT | Wind Advisory | LWX | 30 hr |
| Oct 31, 11:24 PM EDT | Frost Advisory | LWX | 7 hr |
| Nov 9, 2:17 AM EST | Freeze Watch | LWX | 24 hr |
| Nov 9, 1:43 PM EST | Freeze Warning | LWX | 15 hr |
| Nov 10, 2:41 AM EST | Freeze Warning | LWX | 31 hr |
| Nov 18, 3:40 AM EST | Wind Advisory | LWX | 33 hr |
| Dec 8, 5:50 AM EST | Winter Weather Advisory | LWX | 51 hr |
| Dec 24, 10:35 AM EST | Wind Advisory | LWX | 26 hr |
| Dec 26, 9:30 PM EST | Winter Weather Advisory | LWX | 10 hr |
By product
Every kind of product issued here, grouped by hazard. Each opens the same place narrowed to that product.
| Product | Alerts |
|---|---|
| Severe storms | |
| Severe Thunderstorm Warning | 41 |
| Tornado Warning | 1 |
| Severe Thunderstorm Watch | 10 |
| Mesoscale Discussion | 31 |
| Special Weather Statement | 4 |
| Flooding | |
| Areal Flood Warning | 1 |
| Flash Flood Warning | 2 |
| Flash Flood Watch | 4 |
| Winter | |
| Winter Storm Warning | 1 |
| Winter Storm Watch | 1 |
| Freezing Rain Advisory | 1 |
| Winter Weather Advisory | 7 |
| Heat | |
| Heat Advisory | 2 |
| Cold | |
| Freeze Warning | 3 |
| Freeze Watch | 2 |
| Frost Advisory | 6 |
| Wind and dust | |
| High Wind Warning | 1 |
| High Wind Watch | 1 |
| Wind Advisory | 10 |
| Fog and smoke | |
| Dense Fog Advisory | 6 |
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.