Monday, 1 April 2013 | Weather
It’s still absurdly cold for the season. March ended -7.4 degrees F. below normal, with only three of the 31 days modestly above normal in average temperature.
Here is an animated graphic from the Climate Prediction Center showing a North polar view of the earth, with warm and cold air (red and blue) battling for contention in the arctic. This is technically a map of mid-level atmospheric height anomalies, showing ridging (warm at surface) and troughing (cold at surface) over the past month. “500-hPa” refers to the mid level of the atmosphere, roughly halfway from the ground to the tropopause.
Notice how strongly and repeatedly warm air intrudes across the arctic, pushing the cold, blue regions down into the temperate latitudes and squarely into our region of North America. This is a classic “negative phase” of the Arctic Oscillation or Annular Mode.