何月に最も竜巻の危険があるか。その答えはそれぞれの州による。
アメリカ国立気候データセンター (NCDC)による、1991年から2010年までのデータは、竜巻発生頻度の月平均を州ごとに表している。当局は「国全体に該当する竜巻シーズンというものはない」と説明した。むしろ、竜巻の可能性というのは、月と州によって大きく異なるのだ。
竜巻の年間平均 【インフォグラフィック解説】
日照時間の増加と暖かい気候に伴い、アメリカ中部では竜巻は春に活発化する。このNCDCのデータによれば、竜巻が発生しやすい地域では竜巻平均数が春の暮れか初夏にピークをむかえる。アメリカ合衆国は世界の中でも他国より竜巻によく見舞われる。その年間平均は1000以上である。
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関連記事
2014 Tornado Season
Widespread Damage And Casualties After Tornadoes Rip Through South(01 of27)
VILONIA, AR - APRIL 29: An Arkansas National vehicle patrols the tornado stricken area, on April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms are expected over the next few days. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through South(02 of27)
VILONIA, AR - APRIL 29: John Folked uses an electric saw to cut downed power lines where his Realty business once stood before a tornado destroyed it two days earlier, on April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms are expected over the next few days. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through South(03 of27)
VILONIA, AR - APRIL 29: A passerby stops to look at damage caused by a tornado on Sunday evening, on April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms are expected over the next few days. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through South(04 of27)
VILONIA, AR - APRIL 29: The remains of a large truck destroyed by a tornado on Sunday evening rests amid the debris, on April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through South(05 of27)
VILONIA, AR - APRIL 29: Volunteer Gina Lowe (C) helps a family move belongings from a home that was destroyed by a tornado on Sunday, April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms are expected over the next few days. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through South(06 of27)
VILONIA, AR - APRIL 29: A police officer walks past an overturned car at a homesite that was destroyed by a tornado on Sunday, April 29, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Mark Wilson/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(07 of27)
VILONIA, ARKANSAS - APRIL 28: A home lies in ruins after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(08 of27)
VILONIA, ARKANSAS - APRIL 28: A destroyed is shown after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(09 of27)
VILONIA, ARKANSAS - APRIL 28: A home lies in ruins near a storm shelter in the foreground after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(10 of27)
VILONIA, ARKANSAS - APRIL 28: Boots are shown placed on a destroyed brick wall after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(11 of27)
VILONIA, ARKANSAS - APRIL 28: Volunteers load water at Beryl Baptist Church after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(12 of27)
VILONIA, ARKANSAS - APRIL 28: Ken Sullivan, general manager of We Willies Super Auto Wash, looks over the damage after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(13 of27)
VILONIA, ARKANSAS - APRIL 28: Eric Baker and Ron Smith use chainsaws and cut up trees after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(14 of27)
VILONIA, ARKANSAS - APRIL 28: A boy plays in the water where the double wide trailer of Dennis King use to sit before a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(15 of27)
A home lies in ruins near a storm shelter in the foreground after a tornado yesterday tore through the area for the second time in three years, on April 28, 2014 in Vilonia, Ark. After deadly tornadoes ripped through the region, leaving more than a dozen dead, Mississippi, Arkansas, Texas, Louisiana and Tennessee are all under watch as multiple storms over the next few days are expected. (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(16 of27)
VILONIA, ARKANSAS - APRIL 28: Eric Baker and Ron Smith use chainsaws and cut up trees after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(17 of27)
VILONIA, ARKANSAS - APRIL 28: New Vilonia Intermediate School that was set to open in August is left to ruins after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(18 of27)
VILONIA, ARKANSAS - APRIL 28: Lisa Taney, a volunteer, goes through wedding photos found in the mud near a destroyed trailer after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(19 of27)
VILONIA, ARKANSAS - APRIL 28: Books are stacked on a water heater after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(20 of27)
VILONIA, ARKANSAS - APRIL 28: A boy plays in the water where the double wide trailer of Dennis King use to sit before a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(21 of27)
VILONIA, ARKANSAS - APRIL 28: Flag that was found in debris was placed by volunteers working to help clean up after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(22 of27)
VILONIA, ARKANSAS - APRIL 28: Tire punctured by a board sits upside down after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(23 of27)
VILONIA, ARKANSAS - APRIL 28: Flag that was found in debris was placed by volunteers working to help clean up after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Widespread Damage And Casualties After Tornadoes Rip Through Arkansas(24 of27)
VILONIA, ARKANSAS - APRIL 28: New Vilonia Intermediate School that was set to open in August is left to ruins after a strong tornado went through the area on April 27 for the second time in three years on April 28, 2014 in Vilonia, Arkansas. After deadly tornadoes ripped through the area and have left over a dozen dead, Mississippi, Arkansas, Texas, Louisiana, and Tennessee are all under watch as multiple storms over the next few days are expected. (Photo by Wesley Hitt/Getty Images) (credit:Getty Images)
Tornado hits Mayflower, Ark.(25 of27)
Travel trailers and motor homes are piled on top of each other at Mayflower RV in Mayflower, Ark., Sunday, April 27, 2014.A powerful storm system rumbled through the central and southern United States on Sunday, spawning tornadoes. (credit:AP)
Tornado hits Mayflower, Ark.(26 of27)
John Ward, an automobile and RV dealer, looks an tornado damage to one of his trucks in Mayflower, Ark., Sunday, April 27, 2014. A tornado struck the dealer\'s on lot Sunday. (credit:AP)
Tornado hits Mayflower, Ark.(27 of27)
A man walks past a wrecked automobile and RV on Interstate 40 in Mayflower, Ark., Sunday, April 27, 2014. A powerful storm system rumbled through the central and southern United States on Sunday, spawning a massive tornado. (credit:AP)