The 2017–18 North American cold wave was an extreme weather event in North America in which record low temperatures gripped much of the Central, Eastern United States, and parts of Central and Eastern Canada. Starting in late December as a result of the southward shift of the polar vortex, extremely cold conditions froze the eastern United States in the last few days of 2017 as well as into the new year. Following a brief respite in mid-January, cold temperatures swung back into the eastern U.S. shortly afterwards. The cold wave finally dissolved by around January 19, as near-average temperatures returned. Several winter weather events accompanied the cold wave, the most significant one was a powerful blizzard that impacted the Northeastern U.S. in the first few days of 2018. Some of these events impacted areas that normally do not receive snow, such as Louisiana and Texas. In an extremely rare event, Tallahassee, Florida in extreme north Florida received trace amounts of frozen precipitation for the first time in more than 30 years. In addition, many places broke records for coldest temperatures in the final week of 2017 and the first part of 2018.
History
Like most normal cold waves, the cold wave was caused by the southwards movement of the polar vortex into the United States due to changes in the jet stream in late December 2017. Because of an "omega" block pattern that set up around Christmas time – a shift to a pattern with a ridge settling over the western continental U.S and a trough in the central- to eastern parts of the U.S, below-average temperatures occurred through much of the Lower 48 for the final week of 2017 – leading to many records being broken. The pattern continued into the first week of 2018, with more record lows being set following a significant blizzard that impacted the Northeastern United States in early January. By January 11, warmer temperatures had surged northeastwards, although following a winter storm a few days later, cold temperatures returned to the Northeast. The cold wave had an impact on New Year's Eve celebrations in the affected regions; some Canadian cities chose to scale back their ancillary outdoor festivities, including Calgary, Ottawa, and Toronto, although the CBC reported that Montreal and Winnipeg decided to go on without any changes. New Year's Eve celebrations at New York City's Times Square were the second-coldest on record, at .
