Deke Arndt, Climate Monitoring Branch Chief, National Climatic Data Center
During March 2013, a broad swath of the country from the Great Lakes to Florida experienced very cold temperatures — for some states even colder than during January.
Big swings in temperature are often associated with signature pressure patterns. One of these is the Arctic Oscillation, which contributed to the late winter punch leading into Spring this year.
The Arctic Oscillation, or “AO”, is an index describing the difference in pressure between polar locations and mid-latitude locations. It quantifies a pressure pattern often associated with major cold air outbreaks in the mid latitudes, or whether polar air is confined to the higher latitudes.
A positive AO is often associated with fewer polar air masses plunging into our part of the world. But when the AO switches to its negative phase, frigid air can flow out of the Arctic and bring unusually cold weather farther south. In March 2013, the AO was, at times, about as negative as it’s been for decades, especially for the month of March, and we saw some bone-chilling outcomes in the Midwest.
A year ago, the nation experienced its warmest March on record. Look how hot it was across the country in March 2012, compared to how cold it was this year.
During March 2013, a very negative AO phase accompanied colder-than-average temperature in the United States — much colder than it was a year ago, when, you guessed it, the AO was largely positive.
The AO is difficult to predict beyond a week or two, but it can have a dramatic impacts in the United States, across Europe, or in northern Asia.
Even in a warming world, we will continue to have many natural cycles, like the Arctic Oscillation, that drive regional temperatures in the short term. Understanding these phenomena, and how they relate to what we experience, is Climate Smart.
From Asheville, North Carolina, I’m Deke Arndt.
In stark contrast to last year, March 2013 cooler than average in U.S.
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