What is causes it to snow? Repeated storms moving across the country and up the east coast, blanketing all with snowfalls way above average.
Even in Europe, snow has surpassed most “averages” for a good portion of the area. Records are falling there too. What’s going on?
The common denominator here has been very high (and very unusual) high pressure in the upper levels of the atmosphere over the Arctic and Greenland. In Canada, Greenland and Alaska, the temperatures are above average. In the lower portion of Canada (near the Great Lakes), Europe and in most of the USA lower atmospheric pressure has lead to very cold outbreaks and numerous strong storms. Okay… but what causes this to happen ?
Here’s where it gets interesting for weather buffs. The high pressure over Greenland this winter was characteristic of the “negative phase” of the North Atlantic Oscillation and the closely related Arctic Oscillation. Both oscillations refer to seesaw patterns in atmospheric pressure between the polar regions and the middle latitudes (where load of people actually live). In the oscillations’ negative phase, higher than normal pressure areas form over the polar regions and lower than normal pressure troughs from over the middle latitudes. These persistent “troughs” helped stir up storms in that area.