Breaking the U.S. Cold Pattern in the Medium-range

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Fig. 1-3: The Alaska “ridge bridge” pattern is strong this week as supported by the negative phase of the Asian-Bering-North America index. However, the ABNA index goes neutral next week. The ABNA pattern change flips the U.S. pattern from cold to milder.    

Discussion: The first well-established negative phase of the Asian-Bering-North America (-ABNA) of the 2021-22 cold season is intact this week (Fig. 1). The pattern leads to cross-polar arctic air flow into the North America longwave trough pattern (Fig. 2) which delivers frigid weather this week that eventually modifies but reaches the Gulf Coast. However, next week the -ABNA pattern eases and goes flat. During that transition the inflow of cross-polar arctic air is cutoff. Instead, a milder (Pacific) zonal flow develops and leads to a milder U.S. pattern. ECM ENS is particularly mild in the East in the 11-15-day period (Fig. 3).