by EFAS Meteorological Data Collection Centre

July 2021 was characterized by recurring severe weather, causing many as well as extreme floods. Around normal mean sea surface pressure appeared nearly everywhere across the EFAS domain. Slightly lower than normal mean sea surface pressure occurred southwest of Great Britain and Ireland, whereas higher than normal sea surface pressure was observed around Scandinavia and eastern Europe. Monthly precipitation totals were above the long-term mean in central and western Europe as well as around the Black Sea and below normal over the remaining part of the EFAS domain. The monthly mean air temperature was lower than the mean in the northeast of the EFAS domain and western Europe and higher than the mean over the rest of the EFAS domain.

At the beginning of July, a low-pressure system was located north of the Azores. Another low-pressure system was situated over the southern Baltic Sea and a high-pressure system over the Norwegian Sea. The high-pressure system moved to Northern Scandinavia, while the low-pressure system vanished at the surface, but remained in the upper levels and moved eastward. Due to the unstable atmospheric stratification, many heavy precipitation events were triggered (this applies also to the other low-pressure systems mentioned below). The above-mentioned low-pressure system moved from the Atlantic Ocean to Great Britain and Ireland. It was associated with an upper-level trough, which swung eastwards and triggered many severe thunderstorms at its eastern edge. In the meantime, the high-pressure system moved from Scandinavia to western Russia. While this high-pressure system weakened, several upper-level low-pressure systems moved from the Atlantic Ocean to western and central Europe. Some days earlier, a low-pressure system developed over northern Canada. It moved via the Atlantic Ocean and the Bay of Biscay to central Europe, causing severe floods in these regions, and later shifted further towards the Balkans, also associated with severe weather also there. In the same days, the Azores High moved to Great Britain and Ireland and a low-pressure system moved from the Greenland Sea to the Arctic Ocean. The high-pressure system weakened but extended eastwards to central and eastern Europe. While the high-pressure system moved eastward, a low-pressure system moved from the Atlantic Ocean via the Bay of Biscay to the North Sea. It weakened and merged with another low-pressure system from the Atlantic Ocean over Great Britain and Ireland. It split into two cores, one moved via southern Scandinavia to the northern Baltic Sea by the end of the month. The other and smaller core remained at Great Britain and Ireland and moved later across the North Sea to southern Scandinavia. Furthermore, the Azores High was around its usual position by the end of July. The African and south-eastern parts of the EFAS domain were characterized by high pressure with weak gradients over the whole month.

The highest precipitation totals were observed in the Alps and over central Europe (Figure 1). No or almost no precipitation fell around the Mediterranean Sea, as well as in the African and Middle Eastern parts of the EFAS domain. Monthly precipitation totals above the long-term mean occurred in western and central Europe, around the Black Sea, and in southern Scandinavia (Figure 2). Monthly totals below the long-term mean were reported over the Iberian Peninsula, Iceland, Northern Scandinavia, the eastern part of eastern Europe, and around the Mediterranean Sea.

The monthly mean air temperature ranged from -0.9°C to 39.2°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 -10.7°C to 8.7°C (Figure 4). Monthly mean air temperatures below the long-term mean occurred in western and central Europe as well as in the north-eastern part of the EFAS domain, while positive temperature anomalies appeared in the remaining part of the EFAS domain.