Snowfall - snowfall

Snow that has fallen onto electric wires and branches. When snow accretion is particularly likely, it is called electric wire snow accretion. When snow accretion damage is expected, each meteorological station issues a snow accretion warning, which is a type of weather advisory. The main damage caused by snow accretion is the weight of snow that has adhered to communication and power lines, and the phenomenon of snow jumping up when it falls (called sleet jump), which causes electric wires to break, short circuits, and tilt or breakage of electric poles and supports. Wet snow (wet snow) that falls when the temperature is between 0 and 1.5 degrees Celsius and the wind speed is less than 5 meters per second is more likely to accrete. After a certain amount of snow accretion has occurred, it will continue to accrete even if the temperature drops to around -2 to -4 degrees Celsius. It grows cylindrically around the electric wire, is called "tube snow," and can reach a diameter of 8 to 10 centimeters. Snow accretion damage is most likely to occur from November to April, with most occurring in January in the mountainous areas of the Kanto and Chubu regions, and in Aomori, Iwate, and Miyagi prefectures, and most occurring in December in Akita and Yamagata prefectures. In Hokkaido, where powdery snow falls during the coldest period, snow accretion is less likely to occur, and most occurs in early spring. In areas west of Kanto on the Pacific coast, most damage occurs from January to March.

[Atsushi Kurashima]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

電線や枝などに降雪が付着すること。とくに電線の場合を電線着雪という。着雪害が予想される場合には、各気象台は、気象注意報の一種である着雪注意報を発表する。着雪害のおもなものは、通信線や送電線に付着した雪の重みや、着雪が落下するときの電線の跳ね上がり現象（スリートジャンプという）による電線の切断、短絡、電柱、支柱などの傾斜や折損などである。気温が0℃から1.5℃で風速毎秒5メートル以下のときに降る湿性の雪（ぬれ雪）が着雪をおこしやすい。ある程度着雪がおこったあとは、気温が零下2～零下4℃ぐらいになっても着雪は進行する。電線を中心に円筒型に成長し、「筒雪(つつゆき)」とよばれ、直径が8～10センチメートルに達することがある。着雪害の発生しやすい期間は11月～4月で、関東、中部地方の山岳地帯と青森、岩手、宮城県などは1月に多く、秋田、山形県は12月に多い。北海道は最寒期は粉雪が降るので着雪はおこりにくく、春先に多い。関東以西の太平洋側の地方は、1～3月に多い。

［倉嶋　厚］

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