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- Snow Advancing Index - The rate of change in the snow cover over Siberia which can be used to help predict the Arctic Oscillation.
- Arctic Oscillation (AO) - A large-scale weather pattern that affects the circulation in the atmosphere. When the AO is in a positive phase, air pressure is lower than normal over the Arctic and higher over places like the USA, helping to bring about a milder winter. When the AO is in its negative phase, the air pressure over the Arctic is higher than normal and lower over the USA which pushes more cold air further south, helping to bring out harsher winters.
Inside Science Extra: What Does the Snow Advance Index (SAI) Tell Us About This Winter’s Forecast?
According to Dr. Cohen, the SAI for October 2012 is 2.19 ( >2). This high value indicates the negative phase of the Arctic Oscillation which means that more severe winter weather across the Eastern USA is predicted.