The winter regime at NASP is affected by the jet stream
migration to the south, with the continental-polar air mass extending further
to the south. The migration of the jet stream allows an interaction between
the continental-polar air mass and the maritime-tropical air mass. Such
interaction gives rise to mid-latitude cyclogenesis, and the tendency of
the warm, moist maritime-tropical air mass to flow over the colder, drier
continental-polar air mass.