The Winter 1985 cold wave was a meteorological event, the result of the shifting of the polar vortex further south than is normally seen. Blocked from its normal movement, polar air from the north pushed into nearly every section of the eastern half of the United States and Canada, shattering record lows in a number of areas. The event was preceded by unusually warm weather in the eastern U.S. in December 1984, suggesting that there was a build-up of cold air that was suddenly released from the Arctic, a meteorological event known as a Mobile Polar High, a weather process identified by Professor Marcel Leroux.
From Sunday, January 20, to Tuesday, January 22, 1985, the polar vortex, coupled with a large ridge of high pressure, moved polar air into the United States as far south as Florida. Unlike most cold air systems, a pattern of self-modification did not immediately occur, i.e. seasonable temperatures were absent for a number of days, a rarity in forecasting.
The Arctic air mass started moving into the United States on the evening of January 19 and the morning of January 20. An early victim of the air mass was the city of Chicago, which recorded a record low of -27 °F (-33 °C), coupled with 25 miles per hour (40 km/h) winds to produce a wind chill of -77 °F (-61 °C), also never recorded before. The wind chill calculation was adjusted in 2001, which would make the value about -60 °F (-51 °C) on the new scale.St. Louis saw a low of -18 °F (-28 °C). Pittsburgh woke up that morning to find a low of -18 °F (-28 °C), the coldest morning since 1899. In Cincinnati, the morning temperature of -21 °F (-29 °C) tied for the fourth-lowest minimum temperature in the city's history, outdone by a cold mass the year before and a blizzard in 1977.Cleveland fell to -18 °F (-28 °C), which was at the time a record.Memphis recorded a low of -4 °F (-20 °C), setting a record low for that day. The coldest temperature in the contiguous states on Jan. 21 was -24 °F (-31 °C), in the unlikely locations of Akron, Ohio and Knoxville, Tennessee.
The mass moved east and south during the day on January 20, resulting in frigid air for most of the Eastern Seaboard starting on the morning of January 21. New York City's Central Park recorded a low of -2 °F (-19 °C), breaking that date's record.Washington National Airport set a record of -4 °F (-20 °C) for the morning of January 21 and a record low for the prior date of -2 °F (-19 °C). It was the Southern United States that felt the biggest brunt, unaccustomed as they are to the Northern states' winter air. Roanoke, Virginia set a record low of -11 °F (-24 °C), and the campus of the University of Tennessee at Knoxville, Tennessee, recorded a record low of -24 °F (-31 °C). Tennessee's state capital, Nashville, dropped to -17 °F (-27 °C), while all-time records were set well into interior sections of the deep South, such as -5 °F (-21 °C) in Charlotte, -6 °F (-21 °C) in Macon, Georgia, 7 °F (-14 °C) in Jacksonville, Florida, and 10 °F (-12 °C) in Gainesville, Florida (coldest since 6 °F (-14 °C) in 1899). Atlanta saw a low of -8 °F (-22 °C), setting a record for the month of January and for the 20th century, missing by just one degree the all-time record (since 1879) set in February 1899. Even Miami, whose average low in late January is 60 °F (16 °C), recorded a low of 34 °F (1 °C) on the 21st and 30 °F (-1 °C) on the 22nd, both record lows for the date, the latter being one of only 10 times the city has been that cold since 1895.
Ferocious cold in February 1985 set two more state record lows in the Mountain West. Utah's -69 °F (-56 °C) was the second-coldest temperature ever recorded in the "lower 48" states, just above Montana's record of -70 °F (-57 °C) in 1954. Colorado's -61 °F (-52 °C) broke the old record of -60 °F (-51 °C), also on February 1.
The cold wave brought human fatalities, deaths of wild and domesticated animals, crop losses, and infrastructure damage to homes, municipality and industrial sites. At least 126 deaths were blamed on the cold snap. Some 90 percent of the citrus crop in Florida was destroyed in what the state called the "Freeze of the Century." Florida's citrus industry suffered $1.2 billion in losses ($2.68 billion in 2016 dollars) as a result of the inclement weather.  The public inauguration of President Ronald Reagan for his second term was held in the Capitol Rotunda instead of outside due to the cold weather, canceling the inaugural parade in the process. Since Inauguration Day fell on a Sunday, Reagan took a private oath on January 20 and the semi-public oath on January 21.