Late spring (May) is prime time for tornadoes across the U.S., but these destructive vortices don’t exactly hibernate over the summer. Let’s take a look at where tornadoes strike most in the hottest months of the year.
Map 1. Every summer tornado track since 1950
This map shows where tornadoes have occurred since 1950 in the months of June, July, and August. Every state in the Lower 48 has recorded at least one summer tornado.
In the tornado-prone areas of the Southeast, the summer threat is lower than spring. Since the spring, core tornado activity has left the Southeast, and shifted to the Upper Midwest, in a belt from the panhandle of Texas to northern Wisconsin.
Some other things to note on this map:
* A cluster of weak tornadoes focuses around the Denver area. These are twisters that spin up along Colorado Front Range. In part due to its large size and in part due to its position along the Front Range, Weld County, Colorado has the top county tornado count in every summer month: 86 in June, 59 in July, and 31 in August.
* It’s tornado season in the Mid-Atlantic and the Northeast, located on the eastern side of that belt spanning the northern part of the country. Maryland has recorded 173 tornadoes during summer and Virginia has 256 on the books. D.C. has not reported a summer tornado.
* The 10 states with the greatest summer tornado counts are:
Texas – 1,983
Nebraska – 1,454
Kansas – 1,381
Colorado – 1,343
North Dakota – 1,240
Minnesota – 1,206
South Dakota – 1,200
Florida – 1,184
Iowa – 1,111
Wisconsin – 831
* Florida makes the summer top 10 tornado count list thanks to tropical systems that can produce tornadoes in their spiral rain bands.
* The longest tornado track in the dataset is an F4 tornado that crossed northern Missouri and southern Iowa on June 7, 1984. This twister was on the ground for 134 miles.
* The deadliest summer tornado was an F4 in central Massachusetts on June 9, 1953. It killed 94 people and injured 1,228.
* One of the two Maryland F4 tornadoes on record happened in June 1998 when an F4 tornado tracked from southern Pa. into western Md, hitting Frostburg.
* There has not been a summer F5 tornado since July 18, 1996 when an F5 hit east-central Wisconsin.
Map 2. June tornadoes
June is the most active of the summer months for tornadoes (intensity and frequency) and - more than the other summer months – geographically concentrated in the Plains, as shown in these cartograms of total tornado count by county by month. The counties are distorted based on their total tornado count in each month relative to a national average. Solid red counties have 25 or more tornadoes in the month shown.
Maps 3 and 4. July and August tornadoes
July and August see a progressive reduction in tornado numbers compared to June but the tornado counts in the Northeast/Mid-Atlantic tick up in July.
Florida tornado activity is steady for the balance of the summer due to those tropical systems spread across the three months.
(The author, Jordan Tessler, is a Capital Weather Gang summer intern)