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Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water, warming the lower layer of air which picks up water vapor from the lake, rises up through the colder air above, freezes and is deposited on the leeward (downwind) shores.〔(【引用サイトリンク】title=NOAA - National Oceanic and Atmospheric Administration - Monitoring & Understanding Our Changing Planet )〕 The same effect also occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, which deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall. The areas affected by lake-effect snow are called snowbelts. These include areas east of the Great Lakes, the west coasts of northern Japan, the Kamchatka Peninsula in Russia, and areas near the Great Salt Lake, Black Sea, Caspian Sea, Baltic Sea, and parts of the northern Atlantic Ocean. A lake-effect blizzard is the blizzard-like conditions resulting from lake-effect snow. Under certain conditions, strong winds can accompany lake-effect snows creating blizzard-like conditions; however the duration of the event is often slightly less than that required for a blizzard warning 〔http://www.nws.noaa.gov/directives/sym/pd01005013curr.pdf〕 in both the US and Canada. If the air temperature is low enough to keep the precipitation frozen, it falls as lake-effect snow. For lake-effect rain or snow to form, the air moving across the lake must be significantly cooler than the surface air (which is likely to be near the temperature of the water surface). Specifically, the air temperature at an altitude where the air pressure is (roughly vertically) should be lower than the temperature of the air at the surface. Lake-effect occurring when the air at is much colder than the water surface can produce thundersnow, snow showers accompanied by lightning and thunder (caused by larger amounts of energy available from the increased instability). ==Formation== There are several key elements that are required to form lake-effect precipitation and which determine its characteristics: instability, fetch, wind shear, upstream moisture, upwind lakes, synoptic (large)-scale forcing, orography/topography, and snow or ice cover. 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「Lake-effect snow」の詳細全文を読む スポンサード リンク
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