A sudden and intense thunderstorm struck Kanuma City in Tochigi Prefecture around 1 p.m. on Monday [3].
The event highlights the volatile atmospheric conditions currently affecting Japan, where extreme heat is rapidly shifting into unstable weather patterns.
Local residents and visitors were forced to seek immediate shelter under a bridge as large black clouds moved in, bringing heavy rain [1]. This type of sudden, localized downpour is commonly referred to as "guerrilla rain" in Japan [1].
The storm followed a day of dangerous temperatures across the country. More than 200 locations nationwide recorded a "scorching day," defined as temperatures exceeding human body temperature [2].
In Yamanashi, specifically in Katsunuma, the maximum temperature reached 39.4 °C on July 20 [1]. The rapid transition from these extreme highs to the sudden storm in Kanuma City was caused by unstable atmospheric conditions [1].
“large black clouds moved in, bringing heavy rain”
The occurrence of 'guerrilla rain' immediately following record-breaking heat suggests a high level of atmospheric instability. When surface temperatures exceed human body temperature across hundreds of locations, the resulting thermal energy can fuel rapid cloud formation and intense, unpredictable precipitation, increasing the risk of flash flooding and urban disruption.
