Everyone’s Winter Went to Europe
Why has winter been so nasty in Europe and mild in North America? The answer is in the oscillations of the atmosphere.
Arctic Oscillation (AO): Has a positive and a negative phase. The positive phase is when air pressure is a bit lower near the North Pole and there is less pressure on the cold air to spill southward. The negative phase is the opposite. The AO flipped from positive to strongly negative around January 20th. About the same time is when the unprecedented winter storms, snow, and cold began battering Europe.
North Atlantic Oscillation (NAO): The NAO has been positive which means the jet stream leaving North America and entering the Atlantic remains strong, preventing cold air from dumping south anywhere west of Europe, leading to warmer conditions over North America.
Pacific North America pattern (PNA): This is the Pacific’s sister to the NAO. This indicates the strength of the jet stream leaving Asia and entering the North Pacific. This then affects where storms hit western North America and blocking patterns over the Pacific Ocean. The PNA became positive around January 15th, which means blocking over the Pacific forced cold air further north into the Arctic regions, also keeping North America warmer.
All three above factors blocked cold air from dropping south between East Asia and the Atlantic Ocean. This helped squeeze arctic air into Europe where the one remaining door was still open for arctic air to spill southward. A blocking pattern over the Atlantic has formed as a result, forcing warmer air towards the pole – even forcing sea ice away from northern Scandinavia. All this puts further pressure to dump arctic air into Europe (see graphic).
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