Over the past days, the Czech Republic and neighbouring countries have experienced severe flooding due to heavy rainfall. This extreme weather event has led to significant damage, with thousands of people evacuated and many homes without power. The primary cause of this flooding is the low-pressure system named ANETT, associated with the “Vb” (five-B) weather phenomenon, which can also be seen on our sea level pressure map.
Meteorologists use Roman numerals to categorize the paths of special low-pressure systems. The Vb weather pattern is a low-pressure system that originates in the northern Mediterranean. This system typically moves northeastward, bringing moist air from the Mediterranean into Central Europe. The Vb phenomenon is known for causing extreme precipitation events, particularly when the water temperature of the Mediterranean Sea is warmer than usual.
Currently, the Mediterranean Sea is approximately 3 degrees Celsius warmer than the long-term average for this time of year. This increased temperature allows the low-pressure system to absorb more moisture, leading to more intense rainfall over land. Under normal circumstances, weather in Europe is predominantly influenced by low-pressure systems moving from west to east. However, the presence of cold air masses over western Europe can alter this typical pattern.
In this case, a strong high-pressure system over Scandinavia blocked the usual west-to-east movement of weather systems. This high-pressure system forced the low-pressure system ANETT to take a more southerly route from the North Atlantic, bringing it into direct contact with the warm, moist air from the Mediterranean. The interaction between the cold air over western Europe and the warm, moist air from the Mediterranean created the conditions for condensation within the air mass, triggering heavy rainfall and subsequent flooding. The map on the left shows the accumulated precipitation sums >50mm between Friday (2024-09-13) and Sunday (2024-09-15). The map perfectly shows the distribution and the areas with the largest precipitation sums (visualized in red).
In the higher elevations, particularly in the Alps, the precipitation has been falling as snow, which is visualized on our snow depth map.
With the slow-moving low-pressure system lingering over the region, the snow layer continues to grow each day. However, forecasts suggest that temperatures
will rise in the coming days, potentially accelerating snowmelt and further swelling the already-charged rivers, increasing the risk of additional flooding.
Stay safe!
