Snow - AO Relationship

We have identified a dynamical pathway between the fall snow cover, regional surface conditions, upward wave activity, stratospheric temperature and circulation, and the winter AO. The recent very low values of the AO represent a good example of this cycle. October snow cover was very extensive in Eurasia this year, by the end of the month it was the most extensive this decade and probably the most extensive since 1976. This resulted in very cold temperatures in November across Siberia triggering strong upward wave activity in November, a warming of the stratosphere, and a record low AO in December. Why the AO was so exceptionally negative is not yet clear, but interestingly the previous record low December AO was in 2000 following the second most extensive snow cover this decade. The cold temperatures, which were mostly confined to Siberia in November, expanded in December to include Europe and the US. The entire cycle repeated itself in January leading to another stratospheric warming at the end of January, followed in February by another round of a strongly negative AO and cold temperatures in the Eastern US and Europe and is an important driver in the record snows in the Mid Atlantic States.