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Wednesday, February 06, 2019, 19:00 CET

Cold spell

Midwest of the USA, Canada

End of January 2019

Air temperature at 2 meters, January 29, 2019
Source: NASA

At the end of January, arctic weather plunges into North America, causing temperatures down to -50°C. The Midwest of the USA experienced the sharpest cold spell ("Arctic Outbreak ") in more than 20 years. The wind made the temperatures feel even colder (wind chill below -50°C).

Development of the cold spell

The extreme cold wave in the Midwest can be explained by the fact that part of the polar vortex has now settled unusually far south over Canada and the northern Midwest. Temperatures like in the Arctic are the result. During the nights there were widespread temperatures below -30°C. In Collins Bay (Canada) the lowest temperature of the day was -47.0°C on 30.01. In Chicago the lowest temperatures were -31°C. The cold spell was so severe that all-time records were tied or set at least for four weather stations. What is extremely unusual about this cold wave, however, is that it is accompanied by strong winds. Due to the high wind speeds, the temperature is perceived as even colder, as the warmer air layer close to the body is blown away by the wind. This is also called the wind chill or wind chill effect. The feeling of cold is particularly bad in Minnesota. In Ponsfond, a perceived temperature of -54 °C was registered. The record for Minnesota is -57 °C. At -45°C the skin cools down so quickly that it becomes painful. Frostbites and frostbite on unprotected skin threaten after only a few minutes.

500 hPa geopotential from 24 Jan, 00 UTC to 31 Jan, 00 UTC | Source: Wetter3

There is a persistent rumour that severe cold air break-ins in the USA will also occur in Europe after some time. Although there is no direct connection, it is possible that cold air break-ins in Europe are more likely than usual due to the weak polar vortex and that this gives the impression that there is such a direct connection. In the following week it became indeed with us colder, correctly cold arctic cold air did not come however to us.

Minimum Temperatures (30 Jan, 18 UTC), data source: National Weather Service
Location 12h Minimum Temperatur in °C
30 Jan, 18 UTC
Collins Bay (Canada)
Carberry (Canada)
Yorkton (Canada)
Fargo (North Dakota)
Rochester (Minnesota)
Sioux Falls (South Dakota)
Waterloo (Iowa)
Minneapolis (Minnesota)

The high temperature difference between air and water leads to strong lake effect precipitation especially on the eastern coasts of Lake Superior, Lake Michigan, Lake Hudson and Lake Erie. Although the arctic air hardly brings any moisture, the stations Traverse City-Cherr and Muskegon in the east of Lake Michigan registered 30 cm of fresh snow since January 27.

Total snow amount (30 Jan, 18 UTC), data source: National Weather Service

Location Total snow amount in cm
30 Jan, 18 UTC
Lake Superior Provincial Park (Canada)
Wawa (Canada)
Tobermory (Canada)
Traverse City-Cherr (Minnesota)
Muskegon (Minnesota)
Chicago (Illinois)

Pseudopotential temperature from 24 Jan, 00 UTC to 31 Jan, 00 UTC | Source: Wetter3

Animation 2 meters temperature, Jan 23-29 | Quelle: NASA

Temperature records

During the cold spell in the USA and Canada, some all-time low temperature records were broken (see table). In addition to the all-time records, numerous new monthly and decade records were set or set.
Due to the strong wind the temperature felt much colder (wind chill). Nevertheless, the records set were extraordinary.

City State Date Temperature (°C)
Northwest of Mather
Jan. 30
Jan. 31
Jan. 31
Jan. 31


At least 17 people lost their lives due to the cold spell and numerous frostbites were treated in the hospitals. Some schools in the USA and Canada had closed due to the extreme cold. The delivery of postal items was also interrupted. In Chicago, 21 passengers had to be rescued from a bus because the bus collapsed. The reason was gelled diesel fuel due to the extreme cold.

The science behind the polar vortex

"Arctic Outbreak" is the name given to an eruption of extremely cold Arctic air masses far into southern latitudes. The Midwest of the USA experiences such an "Arctic Outbreak" at the end of January. This is due to the so-called polar vortex. This vortex is formed in winter above the pole, where no sunlight can warm up the atmosphere, so that cold air accumulates. As a result, a strong depression forms, which generates stronger western winds in the northern hemisphere and is called the polar vortex.
Normally, the polar vortex with its center is above the Arctic and is mostly stable. However, if the polar vortex weakens, or even divides, then the partial vertebrae start to stagger and are often pushed into southern latitudes. Strong cold air eruptions far to the south are the result. A sudden stratospheric warming at the end of December could be responsible for the weakening of the polar vortex and a temporary division. Such stratospheric warming usually weakens the polar vortex considerably.

Information about polar vortex | Source: NOAA

Text: CL
06 Feb, 2019

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