September 2021 was characterized by higher than normal sea surface pressure over Scandinavia and close to normal sea surface pressure anywhere else across the EFAS domain. Monthly precipitation totals were above the long-term mean in the western and eastern regions, and mainly below the long-term mean in the central and southern parts of the EFAS domain. Monthly mean temperatures were below the long-term mean in the northern and eastern parts, and above the long-term mean over the southern and western parts of the EFAS domain.

At the beginning of September, a high-pressure system was located over Great Britain and Ireland. A low-pressure system was situated over the Barents Sea and other weak systems over eastern Europe and westward of the Iberian Peninsula. The last-mentioned low-pressure system moved to the central Mediterranean Sea and brought intense rainfall, associated with floods, along its track. The low-pressure system located over the Barents Sea moved to northwest Russia and remained active for a few more days. A new high-pressure system formed over southern Scandinavia and moved south-eastwards to the Caspian Sea. A low-pressure system developed over the Atlantic Ocean and moved to the west of the Iberian Peninsula. Then, it changed its direction to move across Great Britain and Ireland to Scandinavia, where it disappeared. Another low-pressure system moved from the Atlantic Ocean to the Iberian Peninsula and went up in an existing weak trough. This trough was associated with several heavy precipitation events over central and southwest Europe. One more low-pressure system developed over Jutland and moved to eastern Europe. At the same time, the Azores high formed around its usual position. Another high-pressure system was established over the Kola Peninsula. An upper-level low-pressure system was cut off over the Bay of Biscay and moved to the Iberian Peninsula, again associated with heavy precipitation. The low-pressure system located over eastern Europe moved over the northern Baltic Sea and intensified there. It weakens soon as it moved towards Russia. A strong low-pressure system developed over the Greenland Sea and moved to Iceland, associated with strong winds. A new high-pressure system developed over northeast Europe. A trough extended from a low-pressure system located over Iceland towards Great Britain and Ireland. A small low-pressure system was cut-off and moved to Jutland by the end of the month. The Azores high was around its usual position and another high-pressure system was located over northeast Europe. A weak upper-level low-pressure system was located over the Black Sea.

The highest precipitation totals were observed over Iceland, the Norwegian coast, central France, eastwards of the Black Sea, and over eastern Europe (Figure 1). No or almost no precipitation fell over western Anatolia as well as the southern and south-eastern parts of the EFAS domain. Monthly precipitation totals above the long-term mean occurred mainly over eastern and northern Europe but also southwestern Europe and Anatolia (Figure 2). Monthly totals below the long-term mean were reported mainly over central and southeast Europe, as well as over the southern and south-eastern parts of the EFAS domain.

The monthly mean air temperature ranged from -5.0°C to 36.9°C with the highest values in the southern parts of the EFAS domain. The lowest temperature values were reported in the northern and mountainous parts (Figure 3). Air temperature anomalies ranged from -7.6°C to 10.0°C (Figure 4). Monthly mean air temperature values above the long-term mean occurred in western and southern parts of the EFAS domain, while negative air temperature anomalies appeared in the eastern and northern parts of the EFAS domain.