By EFAS Meteorological Data Collection Centre

December 2021 was characterized by lower than normal sea surface pressure over southeast Europe and the Atlantic Ocean, and above normal sea surface pressure over Scandinavia and the African parts of the EFAS domain. Monthly precipitation totals were above the long-term mean in the southeast and western Europe. Sums below the long-term mean were observed mainly in the western Mediterranean region, Scandinavia, and the eastern parts of the EFAS domain. Monthly mean air temperature values were below the long-term mean in the northern and African parts, and above the long-term mean over the remaining parts of the EFAS domain.

At the beginning of December, the Azores high was around its typical position and extended towards northern Africa. A strong low-pressure system was located over northwest Russia and dissipated within the next days while moving to the northeast. A weak low-pressure system was situated over the North Sea. It intensified and moved via Jutland to the Baltics, associated with strong winds and heavy precipitation. An upper-level trough extended towards the central Mediterranean region, forced the development of a weak low-pressure system over the eastern Mediterranean Sea and was cut-off. Another low-pressure system developed northward of Great Britain and Ireland and moved to the North Sea, and later to southeast Europe. At the same time, a high-pressure system developed over northwest Russia. It was associated with a cold wave in European Northern Russia, Scandinavia, and the Baltics as it forced cold arctic air to flow to this region. A small but intense low-pressure system developed over the Atlantic, westward of Great Britain and Ireland. It experienced a rapid intensification while moving to Great Britain and Ireland, associated with very strong winds and heavy rains. It moved towards the North Sea and dissipated quickly. Within the next days, a high-pressure system developed over European Northern Russia and a low-pressure system developed southward of the Alps. The latter one was associated with heavy snowfall in the Alps and later in the Balkans. At the same time, an elongated trough from a low-pressure system over the North Atlantic caused heavy rains and snow at the northern Iberian Peninsula and the Pyrenees. By mid of December, a high-pressure system was established over central Europe and was connected with the one over European Northern Russia and the Azores high. They separated the above-mentioned low-pressure system, now located over the Aegean Sea, from the ones over the North Atlantic. As the high-pressure system over European Northern Russia dissipated and the central European high-pressure system moved to Great Britain and Ireland, low-pressure systems moved from the North Atlantic via Scandinavia to European Northern Russia. The associated trough reinforced the remains of the above-mentioned low-pressure system over the Aegean Sea, bringing heavy precipitation to the eastern and northern coasts of the eastern Mediterranean Sea. Around Christmas, an intense low-pressure system developed over northern Scandinavia, associated with strong winds. It moved later to the northeast and dissipated. In the last days of December, several low-pressure systems developed over the Atlantic Ocean. A high-pressure system moved from the Canary Islands to the Iberian Peninsula. Together, they moved mild subtropical air masses to western and central Europe.

The highest precipitation amounts were observed over the central and eastern Mediterranean region, east of the Black Sea, at the west coast of Scandinavia, Great Britain and Ireland, and at the north coast of the Iberian Peninsula (Figure 1). No or almost no precipitation fell in many African parts of the EFAS domain, east of the Caspian Sea, and the southeast coast of the Iberian Peninsula. Monthly precipitation totals above the long-term mean occurred mainly over southeast Europe, western Europe, and around the eastern Mediterranean Sea (Figure 2). Monthly totals below the long-term mean were reported mainly over Scandinavia, around the Caspian Sea, in central and eastern Europe, and around the western Mediterranean Sea.

The monthly mean air temperature ranged from -26.7°C to 22.2°C with the highest values in the southern parts of the EFAS domain. The lowest temperature values were reported in the northern, eastern, and mountainous parts (Figure 3). Air temperature anomalies ranged from -7.0°C to 8.0°C (Figure 4). Monthly mean air temperature values below the long-term mean occurred in northern and north-eastern Europe, and some regions of northern Africa, while positive air temperature anomalies appeared in the other parts of the EFAS domain.