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Tornadoes are a relatively uncommon occurrence in New Hampshire, with only one or two touching down each year on average. Tornadic events primarily occur in the summer, with July featuring the most confirmed tornadoes. These storms are also more common over southern counties. [1] The region's climate and mountainous topography serve to inhibit tornadic formation; however, conditions can still coalesce for small-scale events. [2] The majority of these tend to be short-lived and weak, with a 1950–1990 average path length of 1.64 mi (2.64 km). The two strongest known tornadoes were rated F3 on the Fujita scale [note 1] and touched down on June 9, 1953, and August 20, 1968. However, a violent tornado on September 9, 1821, is believed to have caused EF4 damage and is considered the worst such storm in New Hampshire history. The early 1960s through the early 1970s featured an unusually active period for the state, with several years having four or more tornadoes; 1963 had nine confirmed tornadoes, the highest of any year. The most recent fatal tornado was an EF2 on July 24, 2008, that killed one person, damaged or destroyed 60 buildings, and impacted thousands of acres of forest. [1]
Since 1950, tornadoes have collectively killed one person, injured forty others, and caused $12.6 million in damage. Inclusive of historical events, there have only been six fatal tornadoes in the state's history: May 23, 1782 (1 death), May 21, 1814 (1 death), September 9, 1821 (6 deaths), July 4, 1898 (3 deaths), July 23, 1946 (1 death), and July 24, 2008 (1 death).
Tornado listings between 1880 and 1949 are primarily based upon research by Thomas P. Grazulis and events from 1950 to the present are obtained from the National Climatic Data Center's storm event database. The works of Grazulis only cover significant tornadoes (F2–5), thus a complete record of events prior to 1950 is not available.
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| Month | Number of tornadoes |
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| November | |
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| Unspecified |
| Date | Counties | Deaths | Injuries |
|---|---|---|---|
| May 23, 1782 | Sullivan | 1 | 1 |
| August 15, 1787 | Strafford | 0 | 2 |
| May 21, 1814 | Hillsborough, Rockingham | 1 | 0 |
| September 9, 1821 | Sullivan, Merrimack | 6 | Hundreds |
| July 16, 1880 | Grafton | 0 | 1 |
| May 16, 1890 | Rockingham | 0 | 0 |
| July 4, 1898 | Rockingham | 3 | 120 |
| July 23, 1946 | Merrimack | 1 | 1 |
| June 9, 1953 | Rockingham | 0 | 15 |
| July 3, 1997 | Cheshire | 0 | 1 |
| May 21, 2006 | Rockingham | 0 | 2 |
| July 24, 2008 | Rockingham | 1 | 2 |
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