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The March 1913 tornado outbreak sequence was a devastating series of tornado outbreaks that affected the northern Great Plains, the Southern United States, and sections of the upper Midwest over a two-day-long period between March 21–23, 1913. Composed of two outbreaks, the sequence first began with a tornado outbreak that commenced in Mississippi early on March 21. Several significant tornadoes occurred, one of which killed seven people in one family and another destroyed much of Lower Peach Tree, Alabama, with 27 deaths all in that town. The tornado at Lower Peach Tree is estimated to have been equivalent to a violent F4 tornado on the Fujita scale, based upon damage accounts. The tornadoes occurred between 0630–1030 UTC, or pre-dawn local time, perhaps accounting for the high number of fatalities—a common trend in tornadoes in the Dixie Alley.〔Robinson, "Natural Disasters", ''Encyclopedia'', p. 584〕 In all, tornadoes in Mississippi, Georgia, and Alabama killed 48 people, perhaps more, that day and injured at least 150 people. March 23, Easter Sunday, was the most violent tornado outbreak to affect the northern Great Plains on so early a date in the year—a record that still stands as of 2012. That day, four F4 tornadoes affected portions of eastern Nebraska and western Iowa, killing at least 168 people. The deadliest tornado of the day was a potent F4 tornado that grew to in width as it passed through northern Omaha, Nebraska, killing at least 94 people in the city proper and three in rural areas. Damage in Omaha reached at least F4, possibly even F5, intensity, though confirmation of F5 damage could not be determined from available evidence. The tornado is the 13th deadliest ever to affect the United States and the deadliest to hit the U.S. state of Nebraska as of 2014. No other violent tornado would affect Omaha for another 62 years. Outside the Great Plains, the outbreak of March 23 also produced two other F4 tornadoes, one each in Missouri and Indiana, including a devastating path more than through southern Terre Haute, Indiana, killing 21 people and injuring 250. In all, the two consecutive outbreaks killed at least 241 people and caused at least 19 tornadoes, though only significant events were recorded and other, weaker tornadoes may have gone undetected. The outbreak sequence also produced seven violent tornadoes, nearly half the documented total of tornadoes for the sequence. Tornadoes struck Nebraska, Iowa, Illinois, Missouri, Michigan, and Indiana. At least $9.68 million in damages were reported. ==23 March meteorological synopsis== A series of potent storm systems traversed the US during March 1913, described by the US Weather Bureau as "...the most extraordinary situation in regards to the weather since the creation of the bureau." Anomalously high moisture had gathered near the US Gulf Coast, as an intense upper level storm system moved in from the west. According to retrospective numerical modeling of this event, a strong cap aloft was in place over the central Plains, as is common as the elevated mixed layer advects eastward from the Rockies. Observations taken at 13Z 23 March 1913 showed that surface low pressure was located in Colorado, and a warm front stretched due eastward from there into Illinois. Morning temperatures near this front were in the 30s. South of the front warmer and moister air was present, but dewpoints in the upper 50s were confined to southern Oklahoma and Arkansas, far away from where the tornadoes were to later occur in eastern Nebraska and western Iowa. As the day progressed, the surface low ejected through Nebraska, with a dry line and trailing cold front. South winds blowing 40-50 knots at times brought the moister air rapidly northward. One of the worst dust storms on record occurred behind the dry line in western Kansas, but in the warm sector the day remained dry until mid afternoon when light showers began to form in central Nebraska. A cooperative observer in Osceola noted that the wind shifted from S to NW at 2230Z (4:30 PM local). Professors at the University of Nebraska at Lincoln noted that the relative humidity there jumped from 53% at 2150Z to 78% at 2230Z, indicating much higher dewpoints had rapidly arrived in Lincoln since the cold front was still to the west near Osceola. They also noted that the surface low passed just to the north of Omaha and was in western Iowa at 01Z 24 March 1913. With all of this observed information, it is likely that the quality moisture required to produce convection strong enough for tornadoes arrived just an hour or two before the strong forcing associated with the surface low pressure and attendant frontal systems. At the time of the tornadoes it is estimated that surface temperatures were in the upper 60s, dewpoints were in the upper 50s, and surface winds were southerly around 25-30 knots. Numerical modeling estimates that 500 hPa flow was around 80 knots from the WSW and that CAPE was from 1000-2000 J/kg. These conditions are similar to those found in other tornado outbreaks. Tornadic storms developed from 5:00-6:00 PM local time and while storm motions were to the NE, the prevalence of tornadic storms moved southward with the dryline/cold front intersection, lasting until 8:00 PM local in NW Missouri. A serial derecho then formed and moved across Iowa and Illinois through the nighttime hours, hitting Chicago in the early morning. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「March 1913 tornado outbreak sequence」の詳細全文を読む スポンサード リンク
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