February 2021: very cold in Europe & North America

By Jochen Kerkmann and Vesa Nietosvaara (EUMETSAT), Ivan Smiljanic (CGI), Andreas Wirth (ZAMG), Scott Bachmeier (CIMSS), Daniel Lindsey (CIRA)

The boreal winter season 2019/20 was the warmest winter season ever recorded in Europe, according to the Copernicus Climate Change Service. With persistent mild weather over Europe, particularly in the north and east, the winter 2019/20 was 3.4 °C warmer than the average winter for the period 1981–2010. The temperature was almost 1.4°C higher than that of the previous warmest winter,  2015/16.

Europeans will also remember winter 2019/20 as having very little snow. For example, in Finland, the south coast (Helsinki area) was almost snow-free over the whole winter, see snow depth in Helsinki with the smallest maximum snow depth ever recorded (Credit: FMI). It was too warm for snow in southern Finland (Helsinki DJF 5.8 °C warmer than 1981–2010 mean). Winter 2020/21 also started mild in Europe, but in January 2021 temperatures started to drop, and on 10 January parts of central Spain saw their heaviest snowfalls in decades. By mid-January, many parts of Europe were blanketed in snow, from Spain up to Russia and from Finland across to Greece. However, most of that snow melted in the second half of January when a series of storms battered western Europe. Only Scandinavia and Russia remained snow covered.

In the beginning of February, north-easterly winds brought cold, arctic air from north Siberia to Scandinavia and further west. The Suomi NPP RGB image from 4 February (Figure 1) shows typical arctic airmass features: cloud streets over open seas and snow-covered land (cyan). Over the Gulf of Finland new sea ice can be seen forming at the coastline (see Figure 2).

In the following days, 6–8 February, the temperature contrast between the arctic air over Scandinavia and northern Europe, and warm air over central/southern Europe increased dramatically, leading to a very dangerous weather pattern (see DWD chart from 00:00 UTC on 7 February), similar (but less severe) to the snowstorm case from December 1978. Several countries, including Germany, The Netherlands, Czech Republic and Poland, issued red alerts for snow/ice (Source: Meteoalarm). Along the stationary front, heavy snowfall (20–40 cm) combined with strong winds, causing chaos on roads and railways.

Figure 3 shows the Meteosat-11 Airmass RGB animation from 6 to 10 February: in total, three cyclones can be seen crossing central Europe, dumping snow on their way, see snow map from 9 February (Credit: Snow Cover extent in Europe). A fourth cyclone was approaching from the west. Because of the blocking cold anticyclone over Scandinavia, all the cyclones took a southern track. Note the bright, white cloud band on 6-7 February over Germany, Poland Ukraine and southern Russia, which is caused by so-called dusty cirrus.

Figure 4 is a snapshot taken from the animation, showing one of the cyclones crossing Germany. On this image, the main conceptual models are marked, such as cold fronts, warm fronts and occlusions. For example, over western Germany, a nice example of a Cold Conveyor Belt (CCB) can be seen.

On 10 February, when the last cyclone of the series passed over northern Italy, skies over UK, Denmark, Germany and the Benelux countries started to open up, leading to a further drop in night-time temperatures. The UK had its lowest minimum temperature since 1995 — Braemar, Aberdeenshire, recorded a temperature of -23 °C (-9.4 °F). In central Germany, a 2 m temperature minimum of -26 °C was meassured (nearly a record).

The Terra MODIS RGB images from 10 February (Figure 5) show similar arctic airmass features to Figure 1 — typical cloud streets over open seas (North Sea)  and snow-covered land (cyan and red, respectively). Due to the lake-snow effect, the entire east coast of the UK was snow covered. Patches of snow can also be seen over Ireland. In France, a snow band crossed the country from west to east.