Winter in Unzen with Silver thaw
Silver thaw appear during the harsh winter season from December to March in areas above 1,100 meters such as Nita Pass, Myoken-dake, Kunimi-dake, and Fugen-dake. On particularly cold days, silver thaw can be seen throughout the area for about 10 to 12 days each month.
Several decades ago, when the cold was severe, silver thaw could be seen even in the hot spring town, but in recent years the frequency of seeing hoarfrost has decreased, perhaps due to global warming.
Silver thaw are ice crystals that form on the branches of trees blown by the north wind. They are formed by winter pressure systems, with west high and east low, clouds, fog, and other factors occurring below freezing. Locally, they are also called "hanabouro" and are loved by the residents. By the way, "jyuhu" seen in the Zao region of Tohoku is different from the silver thaw of Unzen; it is formed when snow sticks to the branches and freezes (snowballs).