Extreme Weather East of the Rockies During Winter 2014–2015

Winter weather, ushered in by an arctic air mass, made an early season appearance across much of the conterminous United States in November 2014. Thanksgiving holiday travel was disrupted by snow and ice storms along the southern edge of this arctic air mass. After a hiatus throughout much of December 2014, arctic air returned with a vengeance to impact the region from the Great Lakes to the Northeast and parts of the Southeast during January and February 2015. Record-breaking monthly and seasonal snowfalls, along with record-breaking daily minimum temperatures and record-breaking monthly mean low temperatures in February 2015 were observed in many locations across the Great Lakes and Northeast, especially where deep snows had accumulated. At the same time, record-breaking warmth was observed in many parts of the Intermountain West and Rockies beneath a persistent western North American upper-level ridge.

The purpose of this presentation will be to put the past winter season into context. This task will be accomplished by showing how the Northern Hemisphere large-scale time-mean and anomaly flow patterns governed the structure and evolution of transient upper-level synoptic disturbances of arctic origin. We will show that the recurvature and extratropical transition of Supertyphoon Nuri in the western Pacific, and its subsequent explosive reintensification as an extratropical cyclone triggered downstream baroclinic development, eastward-propagating Rossby wave trains, high-latitude ridging over western North America, and a deep trough over eastern North America that culminated in a massive lake-effect snowstorm in the Buffalo, NY, area on 18-19 November 2014. We will also show that high-latitude blocking over parts of northeastern Russia and Alaska, a persistent trough over the eastern Pacific, high-latitude ridging over western North America, a deep upper-level trough over eastern North America, and a strong upper-level ridge over the central North Atlantic combined to enable disturbances of arctic origin over northeastern Russia and disturbances of subtropical origin over the eastern Pacific to interact and produce frequent heavy snow events, including blizzards, over parts of the Northeast during the latter part of January and much of February 20-15.