North atlantic ossilation

Positive NAO Index

• The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low.

• The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

• This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland

• The eastern US experiences mild and wet winter conditions

Negative NAO Index

• The negative NAO index phase shows a weak subtropical high and a weak Icelandic low.

• The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway.

• They bring moist air into the Mediterranean and cold air to northern Europe

• The US east coast experiences more cold air outbreaks and hence snowy weather conditions.

• Greenland, however, will have milder winter temperatures