Many a March has featured wild gyrations in temperatures from start to finish, but the extremes of this month and a year ago have given “springtime variability” a completely new meaning. The meteorology behind our current bone-chillingly cold weather is every bit as impressive as that which drove a stunning heat wave exactly one year ago.
Upper level pressure pattern late March 2013 (WeatherBell.com)
These hot and cold events arose from two large atmospheric “blocks,” last year’s – which brought the heat – was anchored close to home while this year’s formed 2,000-plus miles away over Greenland in recent days. It’s this second blocking pattern that is steering sub-zero cold out of the Polar region into the U.S. While much of this chilled air mass over the U.S. is not historically cold, 63 percent more daily snowfall records have been set so far this month compared to March 2012. Additional opportunities for record-setting snow will greet the Midwest and parts of the East in coming days.
514 daily snowfall records were broken in March 2012, primarily across the Western U.S. Through the first two thirds of this month, 847 new records have been set, with the lion’s share of these record-breakers occurring over the Midwest.
Meanwhile, Washington, D.C. – presently running one degree colder than average and near normal precipitation-wise – can expect temperatures to feel winter-like through month’s end. A near-record low value of the Arctic Oscillation (AO) – the climate index that measures the difference in relative pressure between the Arctic and mid-latitudes – is partly responsible for the unseasonable chill.
http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/03/21/record-blocking-patterns-fueling-extreme-washington-d-c-march-weather/
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