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The December 25–28, 2012 North American storm complex was a massive storm system that produced both a tornado outbreak and a blizzard across the southern and eastern United States. On Christmas Day 2012 (December 25), a tornado outbreak occurred across Southern United States. This severe weather/tornado event affected the United States Gulf Coast and southern East Coast over a two-day span. It occurred in conjunction with a much larger winter storm event that brought blizzard conditions to much of the interior United States. In total, 31 tornadoes were confirmed by the National Weather Service in five states from Texas to North Carolina. All but one of the tornadoes that occurred during the outbreak touched down on December 25, with the other occurring the following day in North Carolina. Two of the tornadoes were destructive enough to be rated EF3 on the Enhanced Fujita Scale. At least 16 people died as a result of the related blizzard, and thousands were without power. There were 63 preliminary local storm reports received for tornadoes, including 60 in four states on December 25 alone. Significant tornadoes included a long–tracked EF3 that moved across areas of Mississippi and an EF2 that moved through Mobile, Alabama. The Mobile tornado damaged many homes, businesses, a hospital, and a high school, with estimated damages totaling $1.35 million. ==Meteorological synopsis== On December 24, the Storm Prediction Center (SPC) issued a moderate risk for severe storms, valid for the following day. The moderate risk covered an area stretching from west-central Louisiana to west-central Alabama and was expanded south and west on December 25 to include cities such as Port Arthur, New Orleans, and Mobile. From a meteorological standpoint, a strong upper-level trough moved southeast into Texas from the Rocky Mountains on the evening of the 24th, becoming a powerful, negatively tilted shortwave trough on December 25. In response to the shortwave trough, a surface low formed over south-central Texas by 1200 UTC that morning. Warm, moist air near the surface flowed northward along a warm front extending east from the surface low along the gulf coast on the morning of December 25. Meanwhile, a cold front and dry line had formed to the southwest of the surface low and advanced eastward through the morning, providing a source of lift for convection to form in eastern Texas.〔 Initially, the convection congealed into a quasi-linear convective system while over northeast Texas and western Louisiana, with only a few tornadoes touching down in these areas. Later in the afternoon, enough energy associated with the advancing shortwave trough allowed for the formation of tornadic supercell thunderstorms ahead of the advancing squall line in Louisiana, southern Mississippi, and southern Alabama. Southerly winds near the surface increased, providing strong low level and deep layer wind shear needed for these supercell thunderstorms. Many of the supercells would go on to produce tornadoes. By late in the evening, most storms had congealed into a squall line and weakened due to waning instability. In the early hours of December 25, a mix of rain and snow began to develop as the upper-level trough began to interact with low-level moisture from the Gulf of Mexico. The system intensified as it moved across the southern plains and into the Mississippi Valley on Christmas Day. The system was able to pull in cold arctic air, causing snow and freezing rain in the south (leading to a rare "White Christmas" event for that portion of the country). As the system moved through the Tennessee Valley overnight into December 26, heavy snow continued in the Ohio Valley. A number areas in the Ohio Valley region, including Dayton, Ohio and Miamisburg, Ohio, and other locations, like Arkansas, also experienced thundersnow. As the day progressed, the system brought snow into the Great Lakes region, and a new low pressure center began to develop in North Carolina. Environment Canada also reported that the system began impacting Ontario that day, bringing heavy snow to the province. The system moved into the Northeast early December 27, with the upper-level trough moving just off the coast of the Delmarva Peninsula. At this point, the storm reached its lowest reported central pressure of . As the day progressed, the system began to weaken, with the pressure rising, as it continued to move to the northeast, impacting New England, as the system tracked toward the Canadian Maritimes overnight into December 28. That same day, Environment Canada reported heavy and blowing snow over Montreal, Quebec. Early on December 28, the system moved through Nova Scotia, bringing heavy rain and snow before it moved out over the Atlantic Ocean. During the next couple of days, the system slowly moved into the Atlantic Ocean, before accelerating eastward across the Atlantic on December 30. On December 31, the winter storm was absorbed by another extratropical system, just east of the United Kingdom.〔 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「December 25–28, 2012 North American storm complex」の詳細全文を読む スポンサード リンク
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