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Thundersnow, also known as a winter thunderstorm or a thunder snowstorm, is an unusual〔 Dauna Coulter, NASA () Retrieved on 12-20-2012.〕〔(Christine Dell'Amore, National Geographic News )〕 kind of thunderstorm with snow falling as the primary precipitation instead of rain. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone. Thermodynamically, it is not different from any other type of thunderstorms, but the top of the cumulonimbus is usually quite low. In addition to snow, graupel or hail falls. ==Formation== There are usually three forms of thundersnow: * A normal thunderstorm on the leading edge of a cold front or warm front that can either form in a winter environment, or that runs into cool air, and where the precipitation takes the form of snow. * A heavy synoptic snowstorm that sustains strong vertical mixing which allows for favorable conditions for lightning and thunder to occur. * A lake effect or ocean effect thunderstorm which is produced by cold air passing over relatively warm water; this effect commonly produces snow squalls over the Great Lakes. One unique aspect of thundersnow is that the snowfall acts as an acoustic suppressor of the thunder. The thunder from a typical thunderstorm can be heard many miles away, while the thunder from thundersnow can usually only be heard within a two to three mile radius from the lightning. In the United States, March is the peak month of formation; on average, only 6.3 events are reported per year.〔Patrick S. Market, Chris E. Halcomb, and Rebecca L. Ebert. (A Climatology of Thundersnow Events over the Contiguous United States. ) Retrieved on 01-11-2006. 〕 Thundersnow, while relatively rare anywhere, is more common with lake-effect snow in the Great Lakes area of the United States and Canada, the midwestern U.S., and the Great Salt Lake. Thundersnow also occurs in Halifax, Nova Scotia, sometimes several times per winter season. Bozeman, Montana also sees thundersnow more often than average with these storms typically occurring in April or May. The British Isles and other parts of northwestern Europe occasionally report thunder and lightning during sleet or (usually wet) snow showers during winter and spring. It is also common around Kanazawa and the Sea of Japan, and even around Mount Everest. Low pressure events in the eastern Mediterranean that originate from polar origin cause copious thundersnow occurrences during winter storms, especially over the elevated provinces of Israel and Jordan, including Amman and Jerusalem. When such storms happen at ski areas, these mountains are often evacuated for safety. 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「thundersnow」の詳細全文を読む スポンサード リンク
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