Meteorological Situation for April 2021
by EFAS Meteorological Data Collection Centre
April 2021 was characterized by lower than normal mean sea surface pressure over the Norwegian Sea extending to northern Scandinavia, the Azores expanding towards the Iberian Peninsula, and northwest Africa. Higher than normal mean sea surface pressure occurred over the northern Atlantic Ocean expanding to central Europe with weak positive anomalies over the eastern Mediterranean region. Monthly precipitation totals were above the long-term means in parts of Scandinavia, east and southeast Europe, and the Iberian Peninsula. Abnormally low monthly precipitation totals were observed over the African and Asian parts of the EFAS domain, as well as central and north-western Europe. Monthly mean air temperature anomalies correspond with the mean sea surface pressure anomalies – higher than normal mean sea surface pressure was associated with below-normal mean monthly air temperatures and vice versa.
At the beginning of April, a high-pressure system was located south of Iceland and a low-pressure system was situated at the southern Barents Sea. Two more low-pressure systems characterized by very weak gradients were located over the eastern Mediterranean Sea and west of the Iberian Peninsula. These two systems dispersed while the high-pressure system extended in space and moved south-eastward. In addition, the low-pressure system over the Barents Sea dispersed, but an upper-level trough remained and extended towards eastern Europe. In conjunction with the high-pressure system, it forced a cold air outbreak to central and eastern Europe. Another low-pressure system developed over the Greenland Sea and moved towards northern Scandinavia becoming spatially extended and intensified. It was associated with very strong winds in and around Scandinavia and forced another cold air outbreak to central Europe. A second core that developed over Iceland moved to Scandinavia and merged with the first core. An upper-level low-pressure system was cut off and moved to Anatolia. An upper-level trough developed over the Atlantic Ocean and swung through to central Europe. It forced the development of a small low-pressure system over the northern Adriatic Sea, but this was associated with continuous heavy rainfall. This trough was cut off over eastern Europe and surrounded by high-pressure systems over northwest Africa, Russia, and Great Britain and Ireland. The latter two troughs merged over Scandinavia and moved eastward. The upper-level system was stable for a few days but then moved to the central Mediterranean region. Another high-pressure system moved later from the Atlantic Ocean to Great Britain and Ireland, while a low-pressure system developed over the Norwegian Sea and moved across southern Scandinavia towards Russia. In the last days of the month, weak pressure gradients were all over the EFAS domain with a weak low-pressure system over northern Scandinavia and the Barents Sea.
In April 2021, the highest precipitation totals were observed at the western Norwegian coast, the eastern coast of the Black Sea, the Iberian Peninsula, and to the south of the Alps (Figure 1). No or almost no precipitation fell in the African and Middle Eastern parts of the EFAS domain, and in south-eastern Great Britain and Ireland. Monthly precipitation totals above the long-term means occurred over the Iberian Peninsula, parts of north-western Africa, parts of east and south-eastern Europe, and some regions in Scandinavia (Figure 2). Monthly totals below the long-term means were reported over most of the remaining parts of the EFAS domain.
The monthly mean air temperature ranged from -11°C to 30.3°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 -6.6°C to 10.1°C (Figure 4). Monthly mean air temperatures below the long-term means extended from the northwest to central and south-eastern Europe, while positive temperature anomalies appeared in the Middle East, in northeast Europe, Africa, and the western Iberian Peninsula.