The Arctic Oscillation has many aliases. In California, it is the Yukon Express, the cold northern storm that pushed the Pineapple Express floods down to San Diego. In the East, it is the jaunty sounding Alberta Clipper that sailed to Florida and froze the crops. Whatever its nickname, the Arctic Oscillation is cold, stormy and downright miserable.
Technically, the Arctic Oscillation (AO) is a climate pattern caused by the ring of winds that blow around the North Pole from west to east. When they are strong, they trap the Arctic air mass north of 55°N. That’s north of Edinburgh, Moscow and Ketchikan, Alaska. When they are weak, however, the frozen polar air escapes south and can visit sunny California.
Photo: Power lines sag after a heavy storm like we are experiencing this week. Credit: NOAA/Department of Commerce/National Historic Weather Service
Notice, the climate pattern is an oscillation, meaning it switches from one extreme to another. When the AO is positive, the winds are strong. The Arctic remains cold and southern regions are relatively warm. When the AO is negative, the reverse is true. The polar air mass surges south and the Arctic regions are warmer than normal, with less sea ice. These oscillations can swing from one extreme to another in a matter of weeks.
See image to the right. The top reflects positive AO climate patterns; the bottom reflects negative AO climate patterns.
Over the past few decades the warm positive phase of the Arctic Oscillation has slowly strengthened. Then came last winter and the AO plunged. Last February, the AO index (which measures the air pressure differences that shape the winds) averaged -4.266, the most negative index in over 60 years. “Snowmageddon” slammed the nation and by February 13 every state except Hawaii had snow.
It’s happening again – the AO is negative. California was flooded, Florida was frozen and New York City was flat-out buried in snow. Overseas, Europe was hit with record-breaking cold, causing mayhem for holiday traveling. Beijing was had its heaviest snowfall in nearly 60 years. People died of the cold in India.
The AO is still negative and once again cold and storms will be assaulting the South, the Plains, the Midwest and East Coast. Unfortunately if one looks at NOAA’s Global Forecast System computer models, it looks as if this chilly trend will continue. While these model projections are not always accurate, their outlook is chilling. The 10-day forecast has the oscillation dropping to -3 while the 14-day forecast has it plunge below -5.
This is going to create some exciting weather this week. Please tell us what you are seeing and experiencing!
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.