Flash Flood Warnings in New Hampshire
388 flash flood warnings since 1986. 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 since 1986. Tap one for its archive.
- Flash Flood Warnings
- 388
- Busiest year
- 202359 flash flood warnings
- Average year
- 10over 37 years on file
Over time
By year
Before October 2007 these were issued for whole counties, and a storm crossing three counties was often three warnings; since then one polygon follows the storm. The count changed with the practice, not only with the weather.
By month of the year
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
From 2008 to 2025, 83% of flash flood reports in New Hampshire fell inside a flash flood warning issued on average 93 minutes before, and 46% of the flash flood warnings had no report inside them.
Flash flood warnings by year
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| 2008 | 15 | 7 | 53% | 13 | 62% | 74 min |
| 2009 | 7 | 3 | 57% | 11 | 73% | 78 min |
| 2010 | 1 | 1 | 0% | 1 | 100% | 180 min |
| 2011 | 7 | 5 | 29% | 29 | 79% | 158 min |
| 2012 | 11 | 3 | 73% | 21 | 76% | 97 min |
| 2013 | 36 | 21 | 42% | 58 | 91% | 68 min |
| 2014 | 25 | 14 | 44% | 24 | 75% | 69 min |
| 2015 | 11 | 7 | 36% | 16 | 81% | 43 min |
| 2016 | 6 | 3 | 50% | 8 | 100% | 24 min |
| 2017 | 18 | 12 | 33% | 33 | 91% | 83 min |
| 2018 | 11 | 5 | 55% | 18 | 78% | 77 min |
| 2019 | 6 | 4 | 33% | 16 | 63% | 46 min |
| 2020 | 21 | 7 | 67% | 8 | 100% | 40 min |
| 2021 | 15 | 10 | 33% | 37 | 95% | 124 min |
| 2022 | 1 | 0 | 100% | 1 | 0% | |
| 2023 | 59 | 31 | 47% | 74 | 78% | 103 min |
| 2024 | 13 | 8 | 38% | 45 | 89% | 133 min |
| 2025 | 6 | 4 | 33% | 7 | 100% | 75 min |
Years from 2008, the first full year of storm-based warnings. The year still running is on its own page.
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.
By county
Every county with at least one alert. A county page lists each alert that covered it.
The latest flash flood warnings
The most recent on file, newest first.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 8, 7:22 PM EDT | Flash Flood Warning | GYX | Coos | 2 hr |
| Aug 3, 7:21 AM EDT | Flash Flood Warning | GYX | Hillsborough, Merrimack, Rockingham, Strafford | 4 hr |
| Jun 11, 12:33 AM EDT | Flash Flood Warning | GYX | Carroll, Grafton | 3 hr |
Nearby
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.