A circumpolar vortex, or simply polar vortex, is a large region of cold, rotating air that encircles both of Earth's polar regions. Polar vortices also exist on other rotating, low-obliquity planetary bodies. The term polar vortex can be used to describe two distinct phenomena; the stratospheric polar vortex, and the tropospheric polar vortex. The stratospheric and tropospheric polar vortices both rotate in the direction of the Earth's spin, but they are distinct phenomena that have different sizes, structures, seasonal cycles, and impacts on weather.
The Great Blizzard of 1899, also known as the Great Arctic Outbreak of 1899 and the St. Valentine's Day Blizzard, was an exceptionally severe winter weather event that affected most of the United States, particularly east of the Rocky Mountains. On February 11, Swift Current in present-day Saskatchewan reported a record-high barometric pressure of 31.42 inches of mercury (1,064 mb).
A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criteria for a cold wave are the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year.
The cold wave of January 1977 produced the only known trace of snow in the greater Miami area of Florida ever reported. It occurred following the passage of a strong cold front, in combination with a high-pressure area situated over the Mississippi River Valley. As a result, cold air moved far to the south across Florida, causing both snow flurries and record low temperatures. Most notably, the weather system brought snow flurries as far south as Homestead on January 19. No snow had ever been reported in southeastern Florida before or since. Damage was most significant to agriculture, as major losses occurred to citrus fruits and tender vegetables. Statewide, agricultural damage from the cold wave totaled to $350 million (1977 USD), and losses overall totaled to $2 billion (1977 USD). One fatality occurred due to an automobile accident in Central Florida, which was related to the cold wave.
The early 2014 North American cold wave was an extreme weather event that extended through the late winter months of the 2013–2014 winter season, and was also part of an unusually cold winter affecting parts of Canada and parts of the north-central and northeastern United States. The event occurred in early 2014 and was caused by a southward shift of the North Polar Vortex. Record-low temperatures also extended well into March.
The 2013–14 North American winter was one of the most significant for the United States, due in part to the breakdown of the polar vortex in November 2013, which allowed very cold air to travel down into the United States, leading to an extended period of very cold temperatures. The pattern continued mostly uninterrupted throughout the winter and numerous significant winter storms affected the Eastern United States, with the most notable one being a powerful winter storm that dumped ice and snow in the Southeastern United States and the Northeastern United States in mid-February. Most of the cold weather abated by the end of March, though a few winter storms did affect the Western United States towards the end of the winter.
The November 2014 North American cold wave was an extreme weather event that occurred across most of Canada and the contiguous United States, including parts of the Western United States up to western California. One of the first events of the winter, the cold wave was caused by the northward movement of an extremely powerful bomb cyclone associated with Typhoon Nuri's remnant, which shifted the jet stream far northward, creating an omega block pattern. This allowed a piece of the polar vortex to advance southward into the Central and Eastern United States, bringing record-cold temperatures to much of the region. In contrast, Alaska experienced above-average temperatures.
In late January 2016, a cold wave struck much of East Asia, parts of mainland Southeast Asia and parts of northern South Asia, bringing record cold temperatures and snowfall to many regions. Sleet was reported in Okinawa for the first time on record, and many other regions saw their lowest temperatures in decades. Snowfall and frigid weather stranded thousands of people across four countries. At least 85 people in Taiwan died from hypothermia and cardiac arrest following a sudden drop in temperature during the weekend of January 22–24. The cold claimed a further fourteen lives in Thailand, and snowstorms resulted in six deaths across Japan. This event was driven by a fast Arctic warming that occurred within the troposphere, forcing the Arctic Oscillation to change phase rapidly from positive to negative, facilitating the atmospheric blocking and associated Siberian high buildup.
The January 2–4, 2014 North American blizzard was a major winter storm that affected much of the East Coast with snow, and frigid temperatures following the storm. The storm had dumped up to 2 ft (0.61 m) of snow in some areas, especially around Boston, Massachusetts.
The February 2015 North American cold wave was an extreme weather event that affected most of Canada and the eastern half of the United States. Following an earlier cold wave in the winter, the period of below-average temperatures contributed to an already unusually cold winter for the Eastern U.S. Several places broke their records for their coldest February on record, while some areas came very close. The cause of the cold wave was due to the polar vortex advancing southward into the eastern parts of the U.S, and even making it as far south as the Southeast, where large snow falls are rare. By the beginning of March, although the pattern did continue for the first week, it abated and retreated near the official end of the winter.
The 2017–18 North American winter saw weather patterns across North America that were very active, erratic, and protracted, especially near the end of the season, resulting in widespread snow and cold across the continent during the winter. Significant events included rare snowfall in the South, an outbreak of frigid temperatures that affected the United States during the final week of 2017 and early weeks of January, and a series of strong nor'easters that affected the Northeastern United States during the month of March. In addition, flooding also took place during the month of February in the Central United States. Finally the winter came to a conclusion with a powerful storm system that caused a tornado outbreak and blizzard in mid-April. The most intense event, however, was an extremely powerful cyclonic blizzard that impacted the Northeastern United States in the first week of 2018. Similar to the previous winter, a La Niña was expected to influence the winter weather across North America.
The December 2017–January 2018 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.
The 2018–19 North American winter was unusually cold within the Northern United States, with frigid temperatures being recorded within the middle of the season. Several notable events occurred, such as a rare snow in the Southeast in December, a strong cold wave and several major winter storms in the Midwest, and upper Northeast and much of Canada in late January and early February, record snowstorms in the Southwest in late February, deadly tornado outbreaks in the Southeast and a historic mid-April blizzard in the Midwest, but the most notable event of the winter was a record-breaking bomb cyclone that affected much of the Central United States and Canada in mid-March. Unlike previous winters, a developing weak El Niño was expected to influence weather patterns across North America. Overall, however, winter of 2018–19 was mild along the mid- and lower parts of the East Coast, the West Coast, and most of the southern Plains. Overall, the meteorological winter of 2018-19 became the wettest on record for the United States.
In late January 2019, a severe cold wave caused by a weakened jet stream around the Arctic polar vortex hit the Midwestern United States and Eastern Canada, killing at least 22 people. It came after a winter storm brought up to 13 inches (33 cm) of snow in some regions from January 27–29, and brought the coldest temperatures in over 20 years to most locations in the affected region, including some all-time record lows. In early February, a concentration of Arctic air colloquially referred to as the "polar vortex" moved west, and became locked over Western Canada and the Western United States. As a result, February 2019 was among the coldest and snowiest on record in these regions. In early March, the cold once again shifted east, breaking records in many areas. In mid-March, the cold wave finally retreated, but combined with above-average temperatures, precipitation, and a deep snowpack, widespread flooding ensued in the Central US.
The 2019–20 North American winter was unusually warm for many parts of the United States; in many areas, neutral ENSO conditions controlled the weather patterns, resulting in the sixth-warmest winter on record, and many areas in the Northeastern United States saw one of the least snowy winters in years. In fact, Baltimore and Islip saw no snow in February for the first time. Some notable events still occurred, such as a powerful blizzard that impacted the Western United States in late November, a series of cold shots in January and February, a snowstorm within the Texas Panhandle and a late-season blizzard in the High Plains.
The 2020–21 North American winter was the most significant winter season to affect North America in several years, and the costliest on record, with a damage total of at least $33.35 billion. The season featured 6 storms ranking on the Regional Snowfall Index scale, with 4 storms ranking as at least a Category 3. Most of the winter's damage and fatalities occurred due to a historic and major cold wave in mid-February. Several other significant events occurred, including a crippling early-season ice storm in the Southern Plains, a powerful nor'easter in mid-December, another major nor'easter in early February, two major and widespread winter storms in mid-February, and a major blizzard in the Rocky Mountains in mid-March. The winter-related events were responsible for at least 358 fatalities, making it the deadliest season since 1992–93. A La Niña pattern influenced much of the winter in North America.
The February 2021 North American cold wave was an extreme weather event that brought record low temperatures to a significant portion of Canada, the United States and parts of northern Mexico during the first half of February 2021. The cold was caused by a southern migration of the polar vortex, likely caused by a sudden stratospheric warming event that occurred the prior month. Temperatures fell as much as 25–50 °F (−4–10 °C) below average as far south as the Gulf Coast. Severe winter storms also were associated with the bitter cold, which allowed for heavy snowfall and ice accumulations to places as far south as Houston, Texas, and contributing to one of the snowiest winters ever in some areas in the Deep South.
The December 1989 United States cold wave was a series of cold waves into the central and eastern United States from mid-December 1989 through Christmas. On December 21–23, a massive high pressure area pushed many areas into record lows. On the morning of the 22nd, Scottsbluff, Nebraska, experienced −42 °F (−41 °C). The next morning, the front pushed temperatures in Houston down into the single digits. On the 24th and 25th, Miami experienced freezing temperatures and Key West tied its December low of 44 °F (7 °C). The wave extended all the way into Mexico's Lower Rio Grande Valley, resulting in tens of millions of dollars in damage to the agricultural sector. The December cold wave was actually the second of the year, after a February cold wave had extended into Texas.
The 2021–22 North American winter was not as significant and record-breaking as the previous winter season. Despite this, several notable and significant events still occurred, including two separate record-breaking tornado outbreaks in mid-December, a significant winter storm in the South in mid-January, a powerful blizzard that impacted the Northeast coast at the end of January and a wide-ranging, significant winter storm that affected most of the eastern half of the country in early February. Additional significant events included a late-season winter storm in March that affected the Appalachian Mountains, and a major blizzard that affected North and South Dakota in mid-April. Addiitonally, a very late out-of-season snowstorm struck the Rocky Mountains in late May. During the season, four storms have been ranked on the Regional Snowfall Index (RSI), although none attained the “Major” category. Similar to the previous winter, a developing La Niña was expected to influence weather patterns across the continent.
The 2022–23 North American winter was an unusually warm winter for the east and an unusually cold winter for the west in North America, as it occurred across the continent from late 2022 to early 2023. The winter season in North America began at the winter solstice, which occurred on December 21, 2022, and it ended at the March equinox, which occurred on March 20, 2023. The first day of meteorological winter began on December 1 and unofficially ended on February 28; winter storms may still occur outside of these limits.
