Strong cold air in the upper atmosphere has withdrawn from Japan, bringing clear skies to the eastern and northern regions of the country [1].

This shift in weather patterns creates a sharp divide across the archipelago, offering a window for outdoor activities in the north while increasing flood and lightning risks in the south.

For residents in Eastern and Northern Japan, the departure of the cold air means daytime conditions will be generally sunny [1]. This weather shift makes it suitable for hanging laundry outdoors [1]. Temperatures in these regions are expected to rise, with Sapporo reaching a high of 26 degrees Celsius [2] and Aomori hitting 25 degrees Celsius [2].

Some areas will experience midsummer heat. Fukui, Fukushima, and Kumagaya in Saitama are all projected to reach high temperatures of 30 degrees Celsius [2].

Conversely, Western Japan, Okinawa, and the Amami islands remain under the influence of a seasonal rain front [1]. This system is expected to bring rain and thunderstorms to these regions [1]. Consequently, maximum temperatures in Western Japan are generally lower than they were the previous day [2]. In Kagoshima, where rain is expected, the high temperature is forecast at 24 degrees Celsius [2].

The transition reflects the typical volatility of the Japanese rainy season, where the movement of cold air masses and stationary fronts dictates regional stability [1].

“Strong cold air in the upper atmosphere has withdrawn from Japan.”

The divergence in weather between the north and south highlights the interaction between the departing cold air mass and the active Baiu (rainy season) front. While the north recovers from cooler temperatures to experience early summer heat, the south remains vulnerable to the heavy precipitation and electrical activity characteristic of the seasonal front, which can lead to localized flooding.