From 2012 to 2013, March Blows Hot, Then Cold
March is finally on its way out, but not before leaving its mark in the unusually cold and snowy weather that affected much of the U.S., Europe, and parts of Asia. The chilly weather has come courtesy of a stuck weather pattern that has repeatedly directed blasts of cold Arctic air southward, while leaving Greenland and northeastern Canada much warmer than average for this time of year.
Think of the Arctic as the Northern Hemisphere’s refrigerator. The blocked weather pattern — which some scientists think may be tied to the rapid warming of the Arctic and the subsequent loss of sea ice cover — has opened the refrigerator door, causing cold air to spill out of the freezer that is the Far North and help develop winter storms in the northern mid-latitudes. One such storm occupied much of the Northern Atlantic on Thursday, stretching from just south of Greenland all the way east to Ireland and Spain.
The cold weather this month has been in stark contrast to last March, when an unprecedentedly long-lasting and intense early spring heat wave sent temperatures soaring into the 80s all the way to the U.S. border with Canada.
The interactive graphic above shows a comparison between the temperature departures from average during March of 2013 (through March 28) and March 2012.
One of the things to note is that although the extent of the warm weather last March corresponds well to the area affected by the cold this year, the magnitude of the warmth during the 2012 heat wave was far greater than the severity of this year’s cold weather.
This can also be seen by examining the number and characteristics of the temperature records set during the warm March of 2012 and the cold March this year.
In March 2012, the ratio of warm temperature records to cold temperature records was extraordinarily lopsided, at about 15 to 1. But in March 2013, cold temperature records are only beating warm records by about a 2-to-1 ratio, according to data from the National Climatic Data Center (NCDC) in Asheville, N.C.
Forecast sea level pressure departures from average from the GFS computer model for March 20, 2013. This shows the large area of unusually high atmospheric pressure over Greenland.
Click on the image to enlarge. Credit: Weatherbell.com.
In March 2012, the ratio of record daily highs to record daily lows was 12.5 to 1, while this year, record daily lows are only leading record daily highs by a ratio just shy of 2 to 1.
To view it another way, in March of 2012 there were 14,013 warm temperature records broken or tied, while this March has seen only 2,623 cold temperature records broken or tied. And, according to the NCDC, during the March 2012 heat wave, there were 21 instances of the nighttime temperatures being as warm, or warmer, than the existing record daytime temperature for a given date.
According to the NCDC, in March 2012, the U.S. had an average temperature that was 8.6°F above the 20th century average for the month, which was the second-largest monthly departure from average of any month since records began in 1895. March 2013 is unlikely to come close to that, although it will likely rank as one of the coldest Marches in more than a decade.
Clearly, the March 2012 heat wave was more intense and unusual than the current cold snap is.
Interestingly, the weather pattern responsible for the heat wave in 2012 is similar to the cold weather pattern in 2013 in one key respect: they both featured strong “blocking” High pressure systems that acted as a traffic light stuck on red, preventing storms from progressing from west to east across the country. The blocking High this year has been located near Greenland, whereas in March 2012, a dome of High pressure parked itself across the eastern third of the lower 48 states for weeks on end.
As Climate Central has reported, blocking patterns are often associated with extreme weather events, from heat waves like the one that occurred last March, to historic cold air outbreaks and blizzards.
Recent research suggests that rapid Arctic climate change, namely the loss of sea ice cover, may be contributing to blocking patterns like we've seen recently. That rapid decline in Arctic sea ice since the beginning of the satellite record in 1979 may be altering weather patterns both in the Far North and across the U.S. Some studies have shown that sea ice loss favors atmospheric blocking patterns such as the pattern currently in place, while others have not shown statistically significant changes in blocking patterns across the Northern Hemisphere, at least not yet. Arctic sea ice extent declined to a record low during the 2012 melt season.
A study published in 2012 showed that by changing the temperature balance between the Arctic and mid-latitudes, rapid Arctic warming is altering the course of the jet stream, which steers weather systems from west to east around the northern hemisphere. The Arctic has been warming about twice as fast as the rest of the Northern Hemisphere, due to a combination of human emissions of greenhouse gases and unique feedbacks built into the Arctic climate system. The jet stream, the study said, is becoming weaker and “wavier,” with steeper troughs and higher ridges, like a meandering river.
As sea ice melts, it exposes darker ocean water, which absorbs more of the sun’s heat, causing the water temperatures to increase. During the fall, the heat that was added to the oceans gets released into the atmosphere as sea ice reforms, and this added heat is bound to change weather patterns somehow (this is a process known as "Arctic Amplification"). The “how” part is what’s open to debate.
Researchers examining the possible links between Arctic warming and the weather in the U.S., Europe, and other areas must contend with the large amount of natural variability that affects winter weather patterns, and the very short observational record of how the atmosphere responded to extreme losses of sea ice. In addition, climate models and observational evidence actually show a reduction in blocking patterns in parts of the Northern Hemisphere, rather than the increase that one would expect given a warming planet with less Arctic sea ice. At the same time, though, some of the strongest Greenland blocking patterns on record have occurred in the past few years. Also, researchers caution that the computer models may not be capturing blocking well at the present time, let alone the future.
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