Northern Hemisphere Late Winter Arctic Air Masses

Discussion: A prevailing arctic air mass remains anchored over Northeast Asia this week but due to southeastward migration and a narrow cross-polar flow this frigid air mass will weaken by late week (Fig. 1). Meanwhile gathering cold emerges in Alaska and the upslope eastern Northern Rocky Mountains in-part due to cross polar arctic airflow. In the 6-10 day period the North America arctic air mass reaches mature stage and surges into the U.S. (Fig. 2). During the 6-10 day period new very cold air is emerging across Northwest Eurasia. In the 11-15 day period the North America arctic air mass retreats to Western Canada and loses some intensity (Fig. 3). Meanwhile the Northwest Eurasia arctic air mass is moderately strong and expanding.  Catalysts for the arctic air mass development is a long-standing negative arctic oscillation and the eventual expansion of snow cover caused by the -AO regime.

Fig. 1: ECM ENS temperature anomaly forecast for the northern hemisphere for days 1-5.

Fig. 2: ECM ENS temperature anomaly forecast for the northern hemisphere for days 6-10.

Fig. 3: ECM ENS temperature anomaly forecast for the northern hemisphere for days 11-15.