The End of Winter 12-13

Long-Lived Winter of 2012-13 Nearing its End...

After a record-setting February-March in terms of snowfall in parts of New England, a February KU blizzard, a near KU snowstorm in early March, and a historic Palm Sunday snowstorm across Missouri and parts of Illinois, the winter season is now coming to a close.

In large part, the revival of winter and then its long-duration in parts of North America was the result of a blocking regime that has now lasted 52 days. That exceptional blocking regime brought the AO below -5.000 for the first time on record after mid-March. Moreover, through today, the AO has averaged -3.173 for March and a figure below -3.000 is extremely likely when the month ends in two more days. That will surpass the current March record of -2.858 from 1958.

Since 1950, there have been only two years during which the March AO averaged -2.500 (1958 and 1962) or lower and only 5 on which it averaged -2.000 or lower (1957, 1958, 1962, 1970, and 1984). The general consensus of the pattern evolution from those years is that April witnessed a break in the cold pattern, with most of those years favoring warmer readings for the second half of the month in large parts where cool anomalies had begun the month.

All said, that pattern evolution supports the idea coming out in the teleconnection analogs of a dramatic pattern change that will likely see the second half of April wind up warmer than normal in much of the area currently enjoying generally colder than normal readings. It appears that the second week of April could witness the start of that transition.

Before then, winter may launch a last-ditch bid to carve its legacy into the memories of those who experienced some of its highlights. The possibility for at least some accumulation of snow exists in such cities as Chicago, Cleveland, Toronto, Ottawa, Montreal, Worcester, and perhaps even Boston. A small chance exists for at least some snowflakes in parts of Pennsylvania eastward to New York City, though that's not assured. An increasingly rare April freeze is also a possibility in New York City. The last time there was a freeze in April there occurred in 2007.

In sum, Spring 2013 appears likely to begin to take hold in the extended range.