Weather tracker: US storms linked to ‘atmospheric river’ phenomenon | Environment

Weather tracker: US storms linked to ‘atmospheric river’ phenomenon | Environment
November 21, 2025

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Weather tracker: US storms linked to ‘atmospheric river’ phenomenon | Environment

Evacuation warnings were issued last week in California as heavy rain brought the risk of flooding and landslides. The storms in the US were linked to a phenomenon known as an “atmospheric river” – a long filament of moisture-laden air that originates above the Pacific Ocean and provides vital replenishment of reservoirs and snowpack along the western coast of the US. However, they can also bring destructive volumes of rain, particularly along coastal areas.

Elsewhere in the US, parts of Colorado experienced some of their longest stretches of snowless days ever this year, with Denver surpassing its third-latest snowfall date this week after recording its highest ever November temperature of 28C earlier in the month. The warm temperatures and lack of snowfall have also forced ski resorts to delay opening until December.

Severe thunderstorms affected much of northern and eastern Australia last week, with more than 11,000 homes losing power due to heavy rain, hail and strong winds last Friday. Humid tropical air from the north helped to fuel the intense storms across much of the region. Additionally, bushfires triggered by lightning were an additional hazard in the plains of New South Wales, exacerbated by hot and windy conditions.

An aerial view of Versa in Italy shows submerged houses after a landslide caused by torrential rain on 17 November. Photograph: Anadolu/Getty

Meanwhile, heavy snowfall was recorded in the high-altitude town of Sukayu in the northern region of Honshu, the largest and most populous island of Japan, with more than 1 metre of snowfall recorded. The intensity and depth of the snowfall was also notable for how early in the season it occurred with some records being broken. Heavy snowfall also affected parts of Hokkaido, the northern-most island of Japan.

And Italy was also affected by extreme rainfall this week, with mudslides resulting in two deaths in the north. The Torre River overflowed its banks after 25cm (10in) of rain fell in about eight hours, resulting in significant flooding in the town of Brazzano di Cormons, in the province of Gorizia near Trieste. About 300 residents in the nearby hamlet of Versa were also forced to evacuate because of the flooding of the Torre River.

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