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The 1998 Comfrey–St. Peter tornado outbreak was an unseasonably-strong tornado outbreak which affected the Upper Midwest region of the United States on March 29, 1998. A strong area of low pressure combined with a warm front and favorable upper-level dynamics to produce 16 tornadoes across the region—14 in Minnesota and two in Wisconsin. Thirteen of the tornadoes in Minnesota were spawned by a single supercell thunderstorm. This supercell remained intact for approximately as it moved across the southern part of the state during the late-afternoon hours. Over $235 million in damage (1998 US$) was recorded from the tornadoes, two people were killed, and 21 others were injured. Most of the damage was caused by three tornadoes—one rated F4 on the Fujita scale that hit the town of Comfrey, Minnesota, an F3 that hit St. Peter, Minnesota, and an F2 that hit Le Center, Minnesota. Gustavus Adolphus College in St. Peter was especially hard-hit, with several buildings damaged or destroyed, 2,000 trees lost, and nearly 80% of the windows on the campus shattered. In Comfrey, 75% of the structures in the town were damaged or destroyed, including the local K–12 school. Seven counties in southern Minnesota were later declared federal disaster areas. The outbreak broke many early-season tornado records for the state of Minnesota. The 14 total tornadoes in the state were the most to ever touch down on a single day in March. The F4 tornado was the strongest ever recorded in the state in March, and its 67-mile (108 km) path the longest tornado path ever recorded in Minnesota. In December 1998, the United States Department of Commerce awarded a bronze medal to the Twin Cities office of the National Weather Service (NWS) for providing excellent service to the public during the outbreak event. ==Meteorological synopsis== The driving force behind this tornado outbreak was a strong surface-based low-pressure area stationed over the western high plains. On the morning of March 29, the low was centered over eastern Wyoming, with a warm front stretching eastward across Nebraska and Iowa. An upper-level trough of low pressure was centered over the southwestern United States, which caused an upper-level jet stream with winds of 100 knots () to push towards Minnesota from the southwest. A low-level jet from the south with winds of transported a plume of warm, humid air into the region, helping to push temperatures above and dew points into the middle 60s °F (around 20 °C).〔 Winds on the surface were from the southeast, which created low-level wind shear; enhancing the potential for tornadoes. By early afternoon, the low-pressure area had moved east into Nebraska, while the warm front had moved northward into southern Minnesota.〔 The atmosphere to the south of the warm front was strongly capped, meaning that the best chance of thunderstorm development was in areas along and slightly north of the front. By the time the thunderstorms started developing, CAPE values were 2000 J/kg, indicating moderate atmospheric instability. Also present were low-level and deep-layer wind shear values of , respectively. All of these factors combined to create very favorable conditions for the development of severe thunderstorms and tornadoes.〔 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「1998 Comfrey–St. Peter tornado outbreak」の詳細全文を読む スポンサード リンク
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