From hot sun to snow in 24 hours. That was the fate of Denver as the seemingly never-ending summer suddenly became winter.

Wednesday was a day of warm sunshine and 26C in Denver, Colorado. Then, on Wednesday night, a major cold front, known as the Polar Front, swept through, and the temperature dropped to 4C before midnight.

It was snowing by Thursday lunchtime and gusting in the northerly wind to 54km an hour by the end of the afternoon. By midnight, 6cm of snow had fallen and the temperature was -6C.

The polar front has been descending across the North American Rockies for the past two days or so, bringing normality to what has been a warm November so far.

The Canadian ski resort town of Banff has finally, and only just, had a day below freezing. On Thursday, the maximum temperature was -0.4C after the previous two nights had frozen the ground to below -10C.

Surge of warm air

North Dakota has also felt the change. Wednesday was a warm 16C but Thursday was restricted to 3C.

In advance of a cold front, a surge of warm air generally lifts temperatures well above normal and this has happened in US states and Canadian provinces.

On Thursday, Chicago, Illinois reached 22C. This was 7C higher than Wednesday and 13 degrees higher than average.

St John's, Newfoundland, enjoyed a summer day at 18.9C. This was 13 degrees warmer than Wednesday, which was an average day for Newfoundland.

Newfoundland will hang on to some warmth, albeit cooled by much rain, for another four or five days. The rest of North America will return to conditions more typical of early winter.

Source: Al Jazeera