A super cold/warm clash of air masses likely to drive extremes for winter 2018-19 Discussion: One does not normally associate historic summer heat and drought with the polar vortex but 2018 is different (Fig. 1). Throughout 2018 the polar vortex has been stronger than normal but at a far northern latitude and biased toward the northern North Atlantic. The result is the strongest and most consistent positive phase of the arctic oscillation and particularly the North Atlantic oscillation on record for 2018 (Fig. 2). The most recent weather extreme caused by this phenomena is the well above normal snow cover (Fig. 3) across Canada (and into the U.S.) and the evolving attendant cold already freezing the Great Plains so far in October and about to shift into the East U.S. for the last third of the month. Couple the deepening early season Canadian snow cover and the associated cold air masses with emerging warm influence on climate by a building powerful El Nino (Fig. 4) and we’re looking a winter ahead likely to bring DRAMATIC thermal changes and intense storms as extreme cold/warm air masses clash. Fig. 1: The most persistent and strong polar vortex on record in 2018. Fig. 2: Except for March the AO and especially NAO has been in the positive phase indicating presence of a strong polar vortex. No year in the 1950-2018 climatology has produced such a consistent positive phase. Fig. 3: The +NAO pattern has caused above normal snow cover across Canada is October causing widening North American chill. Fig. 4: The subsurface equatorial Pacific is immensely warmer than normal offering plenty of fuel for El Nino ahead.