Alert archive / New Hampshire / Flash Flood Warnings
Flash Flood Warnings in New Hampshire, 2009
7 flash flood warnings in 2009. An alert counts here when it covered any part of the state, so the counties below add up to more than the state. The archive of flash flood warnings reaches back to 1986.
Flash Flood Warnings by county
Each county as a circle sized by its count in 2009. Tap one for its archive.
- Flash Flood Warnings
- 7
- Busiest month
- July3 flash flood warnings
- Busiest day
- July 2, 20093 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.
3 of 7 flash flood warnings covering New Hampshire in 2009 had a flash flood report inside them; 8 of 11 flash flood reports fell inside a warning, on average 78 minutes after it went out.
New Hampshire, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Flash flood warnings | 7 | 3 | 57% | 11 | 73% | 78 min |
Each office's whole area, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Boston/Norton, MA: flash flood warnings | 22 | 3 | 86% | 13 | 62% | 68 min |
| NWS Gray, ME: flash flood warnings | 15 | 5 | 67% | 9 | 78% | 108 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 | Counties | Lasted |
|---|---|---|---|---|
| Jun 27, 6:32 PM EDT | Flash Flood Warning | GYX | Belknap, Merrimack | 3 hr |
| Jun 29, 7:34 PM EDT | Flash Flood Warning | GYX | Merrimack | 3 hr |
| Jul 2, 8:41 AM EDT | Flash Flood Warning | BOX | Hillsborough | 4 hr |
| Jul 2, 9:09 AM EDT | Flash Flood Warning | GYX | Belknap, Carroll, Merrimack, Rockingham, Strafford | 3 hr |
| Jul 2, 7:47 PM EDT | Flash Flood Warning | GYX | Strafford | 2 hr |
| Aug 21, 4:02 PM EDT | Flash Flood Warning | GYX | Grafton | 3 hr |
| Aug 22, 6:15 PM EDT | Flash Flood Warning | BOX | Cheshire, Hillsborough | 2 hr |
By county
Every county with at least one alert. A county page lists each alert that covered it.
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordThe radar archive20082010
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.