Thank you for explaining NPM and its relation with ENSO and decadal modes. If I'm understanding correctly from the earlier comment, Winter 1976-1977, the primary culprit for the cold extremes in the late 1970s was La Niña, whereas the primary culprit the past two winters was NPM? Does anyone have an idea why NPM does not always precede El Niño (as described in footnote 3)? Is there any known correlation between NPM and Judah Cohen's hypothesis regarding downstream effects of increasing Siberian snowfall in autumn? Cohen's hypothesis goes something like this, and sounds like a special case of Jennifer Francis's arctic amplification scenarios: Warming global temperatures > extreme Eurasian snowfall in autumn > cold dome near Altai, Himalayas, and Tien Shan > amplification of Rossby waves in Pacific, both stratospherically and longitudinally > more meandering jet stream over North America that winter > lobes of polar vortex frequently breaking off and heading into eastern USA.