noun
first wintry wind of autumn
A seasonal term used in weather forecasts and news to mark the arrival of the first strong, cold wind signaling the transition to winter. Often associated with the Tokyo area.
See also: 木枯らし
気象庁は今日、東京で木枯らし１号が吹いたと発表した。
The Japan Meteorological Agency announced today that the first wintry wind of autumn blew in Tokyo.
木枯らし１号が吹くと、急に冬の気配が強まる。
When the first wintry wind blows, the feeling of winter suddenly intensifies.
Refers to a cold, blustery wind in late autumn to early winter in general. 木枯らし１号 specifically denotes the first such wind of the season as officially recognized by meteorological agencies.
Compound of 木枯らし (こがらし, 'wintry wind') and １号 (いちごう, 'number one'). The term is a modern meteorological coinage.