The Iditarod dog sled race in Alaska has been rerouted because of a severe lack of snow. The Iditarod is the world’s most gruelling sled race, covering 1,600km (1,000 miles) of mountain ranges, frozen rivers, dense forest, tundra and coastline. The official start of the race was moved some 360km north because unseasonably warm weather had left parts of the trail without snow, making the terrain especially dangerous.
In fact, the western states of the US have experienced exceptionally warm weather this winter. More than 20 places had their warmest winters on record, including San Francisco, Seattle, Salt Lake City and Portland, Oregon. Bears came out of hibernation in Yellowstone Park, Wyoming, about a month earlier than usual, in Vancouver cherry blossom made an early appearance and California is so short of water and snow that it is facing a third consecutive year of drought.
However, central and eastern parts of the US were having a long, hard winter. Boston set a new record for heavy snowfall in February with 165cm (65in) of snow — the previous record was 114cm. Huge snowfalls were matched by bitter cold that also set records in many places. Maine had its coldest average temperature for February, at -16C (3.2F). And the snowstorms have continued, with another big storm arriving last Thursday and sweeping across a large part of the eastern US.
The division between east and west was caused by a persistent surge of freezing Arctic air plunging across eastern areas, while warm air came up from the south over western areas. The dividing line between the two air masses was the jet stream, which remained stuck in place for much of the winter. Why this weather pattern persisted is less clear, but there was no El Niño weather system in the Pacific to blame. For the past year it seemed that an El Niño pattern was about to appear, but it has only just begun to emerge, and is expected to be weak.