A weak high, a cut-off low, and rapid ocean warming conspired to dump torrential rains in Chile's Atacama Desert in late March 2015.

Uncommon atmospheric circumstances spawned a pair of tropical cyclones in the western Pacific—one on either side the equator, at nearly the same longitude, at nearly the same time. Why are twin cyclones more common during El Niño?

The extreme atmospheric pressure pattern that favored record-breaking snow totals across parts of the U.S. East left Alaskans asking, “Where’s winter?”


January 2014 was remarkably mild across nearly all of Alaska, resulting in this January ranking among the  “top ten” warmest on record for many Alaskan communities according to preliminary analyses.

The Arctic Oscillation describes simultaneous, geographically “choreographed” shifts in multiple features of the polar vortex: air pressure, temperature, and the location and strength of the jet stream. They all follow the hemisphere-wide oscillation of atmospheric mass back and forth between the Arctic and the middle latitudes, sort of like water sloshing in a bowl.

A few days of unusually cold weather in the U.S. and Canada aren't a sign that a century-or-more trend of rising global surface temperatures has reversed itself. In fact, the cold wasn't even all that widespread for the Northern Hemisphere.

Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Climate scientists are wondering if a warmer Arctic could explain its odd behavior in recent years.

October in Alaska this year was more like September, with warmth and rain in place of autumn chill and snow. Wind anomalies related to unusual pressure patterns conspired to bring a steady stream of warm, wet air from southerly latitudes into Alaska.