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The 1804 Snow hurricane (also known as the Storm of October 1804) was the first tropical cyclone in recorded history known to produce snowfall. An unusual late-season storm in 1804, it yielded vast amounts of snow, rain, and powerful winds across the northeastern United States. Prior to its approach towards the East Coast of the United States, it passed through the Caribbean Sea on 4 October, and later emerged near Georgetown, South Carolina. By early on 9 October, a trough near the Virginia Capes turned the disturbance toward New England. Soon thereafter, the hurricane's abundant moisture clashed with an influx of cold Canadian air, leading to the deepening of the resulting pressure gradient and provoking inland intensification. While situated over Massachusetts, it attained its peak intensity of 110 mph (175 km/h), undergoing an extratropical transition. Even as it drifted towards the Canadian maritimes, consequently gradually weakening, precipitation persisted for another two days before the snowstorm finally subsided on 11 October. Due to its unusual nature, both heavy snowfall and strong winds caused a swath of devastation stretching from the Mid-Atlantic states to northern New England. In the Middle-Atlantic region, moderate damage occurred at sea but little was noted inland. In New England, strong gusts inflicted significant damage to numerous churches. Widespread residential damage, in contrast, was mostly negligible and had no lasting consequences. Thousands of trees were knocked over, obstructing roads and fiscally damaging the timber industry throughout the region. Cold temperatures, wet snow, and high winds downed numerous branches in fruit orchards, froze potato crops, flattened dozens of barns, and killed over a hundred cattle. In general, the agriculture, shipping, timber, and livestock trades suffered most acutely following the passage of the snow hurricane, while structural damage was widespread but generally inconsequential. The storm's most severe effects were concentrated at sea and led to a majority of the hurricane's deaths. Winds swept dozens of watercraft and multiple ships ashore, while high waters capsized many others. Several wharves were destroyed, subsequently harming local shipping businesses as a consequence. Snow and rainfall totals varied widely between states, with a clear delineation between areas that received frozen precipitation and rainfall in the Northeast. Areas of Massachusetts received up to of rain, in contrast to snow totals upward of measured in Vermont. In all, the hurricane caused more than 16 deaths at sea and one inland, and also resulted in at least $100,000 (1804 USD) in damage. The snow hurricane of 1804, generally described as the most severe storm in the United States since the Great Colonial Hurricane of 1635 nearly 200 years earlier, set several major precedents which have only infrequently occurred since. It was the first known tropical cyclone to generate snowfall, and its early and extensive accumulations throughout New England were unprecedented and unusually heavy. == Meteorological history == The origins of the snow hurricane prior to its approach near New England are mostly unknown. Though a modern study conducted in 2006 traced its origins to north of Puerto Rico on 4 October 1804 and reports indicated it also passed by Dominique and Guadaloupe the same day, little else was known about the storm until its approach towards the East Coast of the United States and transit near South Carolina.〔Chenoweth 2006, p. 222〕 Weather historian David Ludlum concluded that both the hurricane's strength and its abnormally cold environment were derived from the influx of unseasonably cold air from the north converging upon the storm's abundant moisture, increasing the pressure gradient and leading to intensification.〔Ludlum 1966, p. 169〕 He also speculated that the storm could have formed non-tropically from the southern Appalachian Mountains before arriving on the Atlantic coast, but given meteorological circumstances, characteristics, and timing, it was evaluated that the storm was of tropical origin.〔Ludlum 1963, p. 35〕 The earliest evidence of a disturbance near the United States was noted on 8 October, when rainfall was recorded in upstate New York, precipitated by the storm's western periphery in advance of an approaching trough.〔〔Ludlum 1963, p. 38〕 The following morning, the trough's motion near the Virginia Capes area was accompanied by intensifying winds and a change in their direction; initially southwesterly force 3, the incoming gale's winds rapidly turned towards the west-northwest, escalating to force 6 by the afternoon.〔 A 2001 study noted the unusual orientation of the storm's winds; although a majority of New England hurricanes induced southeasterly gusts, the 1804 snow hurricane's, in contrast, were mostly southwesterly.〔Boose et al. 2001, p. 39〕 Historical records chronicled the remainder of the storm's track along the East Coast of the United States. A "dreadful squall" occurred near Cape Henry at noon, and historical documents confirm it quickly reached Chesapeake Bay later that morning, maintaining west-to-north winds. While gusts in New York City, where the storm arrived that afternoon, initially blew towards the southeast, they soon shifted towards the north-northwest and coincided with a rapid drop in atmospheric pressure, which bottomed out at 977 mbar (28.87 inHg) by the early afternoon. Though the barometer at the weather station remained at that point for much of the afternoon, the air temperature plummeted rapidly from to during the same period.〔Ludlum 1963, p. 36〕 A strong westerly circulation encouraged the swift eastward movement of the through's northern segment, steering the course of the storm northeasterly over New England.〔Ludlum 1963, p. 37〕 By the evening, the storm had fully traversed the northeastern United States, where accounts indicated the passage of the storm's eye.〔 The results of the 2001 study also suggested atypical strengthening occurred around this time,〔Boose et al. 2001, p. 34〕 achieving its peak intensity with 1-minute maximum sustained winds of 110 mph (175 km/h) over Massachusetts, equivalent to a Category 2 hurricane on the Saffir–Simpson hurricane wind scale. The storm's maximum diameter was estimated to be at its largest point.〔Boose et al. 2001, p. 40〕 As the hurricane weakened throughout the night, it underwent an extratropical transition, evidenced by a passageway of weak winds off of the trough's center. Its eye was consequently distorted as it meandered northward towards Canada, where it subsequently encountered an area of high pressure;〔 though gusts diminished that evening, moderate precipitation persisted for another two days before the snowstorm finally departed on 11 October.〔Perley 1891, p. 168〕 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「1804 Snow hurricane」の詳細全文を読む スポンサード リンク
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