Alert archive / Virginia / Fairfax County / Flash Flood Warnings
Flash Flood Warnings in Fairfax County, Virginia, 2011
18 flash flood warnings in 2011. An alert counts here when it covered this county. The archive of flash flood warnings reaches back to 1986.
Fairfax County and its neighbors
Each county as a circle sized by its count in 2011. Tap one for its archive.
- Flash Flood Warnings
- 18
- Busiest month
- September7 flash flood warnings
- Busiest day
- September 8, 20114 flash flood warnings
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
13 of 18 flash flood warnings covering Fairfax County in 2011 had a flash flood report inside them; 27 of 29 flash flood reports fell inside a warning, on average 107 minutes after it went out.
Fairfax County, 2011
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Flash flood warnings | 18 | 13 | 28% | 29 | 93% | 107 min |
Each office's whole area, 2011
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Baltimore/Washington: flash flood warnings | 170 | 99 | 42% | 341 | 84% | 121 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 |
|---|---|---|---|
| Mar 10, 5:48 PM EST | Flash Flood Warning | LWX | 4 hr |
| Apr 27, 7:21 PM EDT | Flash Flood Warning | LWX | 69 min |
| Apr 28, 9:45 AM EDT | Flash Flood Warning | LWX | 101 min |
| May 18, 3:40 PM EDT | Flash Flood Warning | LWX | 2 hr |
| Jun 17, 12:02 AM EDT | Flash Flood Warning | LWX | 3 hr |
| Jul 13, 3:07 PM EDT | Flash Flood Warning | LWX | 3 hr |
| Jul 13, 3:45 PM EDT | Flash Flood Warning | LWX | 3 hr |
| Aug 18, 5:44 PM EDT | Flash Flood Warning | LWX | 3 hr |
| Aug 19, 7:43 PM EDT | Flash Flood Warning | LWX | 87 min |
| Aug 27, 5:26 PM EDT | Flash Flood Warning | LWX | 9 hr |
| Sep 7, 10:47 AM EDT | Flash Flood Warning | LWX | 7 hr |
| Sep 7, 11:38 AM EDT | Flash Flood Warning | LWX | 3 hr |
| Sep 7, 9:09 PM EDT | Flash Flood Warning | LWX | 3 hr |
| Sep 8, 12:23 PM EDT | Flash Flood Warning | LWX | 11 hr |
| Sep 8, 2:31 PM EDT | Flash Flood Warning | LWX | 5 hr |
| Sep 8, 7:01 PM EDT | Flash Flood Warning | LWX | 4 hr |
| Sep 28, 8:18 PM EDT | Flash Flood Warning | LWX | 107 min |
| Oct 13, 8:53 PM EDT | Flash Flood Warning | LWX | 2 hr |
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordForecastThe radar archive20102012
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.