Atmospheric rivers and the future of skiing

These weeks seem to see a return to the series of atmospheric rivers that were so prevailing last year and my observation is that the water vapor contained in these massive plumes of deep tropical moisture can fall into rain even a local temperature below freezing point (31 degrees) when under normal circumstances it does snow up to 36 degrees. 

These atmospheric rivers, often called “Pineapple Express” originate in the tropical Pacific near Hawaii. They can sometimes carry 15 times the water volume of the Mississippi River, delivering half of the western United States’ total precipitation in less than 15 total days. In general, global warming will push jet streams closer to the equator. 

But with the Arctic region having already warmed by some 6ºC, five times the global average warming, the mean west-east component of the jet streams have weakened, because it is the difference between polar and tropical temperatures that energizes jet streams. If there is less west-east airflow in the jet streams, then there is more potential for the jet streams to meander away from their traditional latitudes. 

This means that the plunges of polar air far southwards, and the streaming of tropical air far northwards, will become more frequent and bring extremes of temperature to places unaccustomed to them. "Heat domes" such as the one over western Canada in June 2021, and western Europe in July 2022 contrast sharply with "Ice bombs" such as the ones recently affecting northern and eastern USA and Canada, and Texas in Feb 2021, may become more frequent, but not necessarily in the same places. 

Overall, though, it seems that our winters, both in North America and Europe are clearly in severe warming trends, and if we factor in, the “Hockey Stick” graph developed by Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes in 1998, reconstructing global or hemispherical mean temperature record of the past 500 to 2000 years, showing a slow long term cooling trend that suddenly turn into relatively rapid warming in the 20th century, with the instrumental temperature record by 2000 exceeding earlier temperatures. 

This warns us that if this trend keeps on going on, any atmospheric river might turn into major bad news if it cannot drop the so important snow for water storage and skier’s enjoyment!