Polar Vortex ALSO Causes Late Winter Heavy Precipitation

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Historic high-level polar vortex of late winter 2018-19 caused BOTH temperature extremes and excessive precipitation

Discussion: The strongest high level polar vortex on record (Fig. 1) dominated northern hemispheric late winter climate and particularly the U.S. pattern. The super intense high level polar vortex emerged in early February. The 30-day arctic oscillation has averaged near +3 St Dev during the past 30 days (Fig. 2) which is near strongest on record. Normally we associate the polar vortex with extreme temperature regimes certainly present across the U.S. during the past 30 days (Fig. 3). However, this time the +AO regime also helped to inspire late winter season excessive precipitation (Fig. 4) helping to ignite an already extreme flood season in the Central U.S.

Fig. 1-2: The 10 MB temperature anomalies for the past 30 days identifies the vigorous cold polar vortex as represented by equally strong positive phase of the arctic oscillation.

Fig. 3-4: The 30-day U.S. temperature anomalies and percent of normal precipitation observations identify extremes brought on in-part by an intense high level polar vortex.