Matalapaineinen

Matalapaineinen is a Finnish adjective used in meteorology to describe weather phenomena or air masses associated with low atmospheric pressure. It is applied to a low-pressure area (matalapaineinen alue) or a low-pressure system (matalapaineinen järjestelmä). The term is used in contrast to high-pressure (korkea­painen) conditions.

A defining feature of matalapaineinen conditions is that the air pressure is lower than in surrounding areas. There is no single fixed threshold, but low-pressure regions are typically characterized by pressure values below the surrounding environment and by dynamic atmospheric processes. The presence of rising air in these regions promotes cloud formation and often precipitation. In the Northern Hemisphere, winds around a low-pressure center tend to rotate counterclockwise, while in the Southern Hemisphere the rotation is clockwise, a consequence of the Coriolis effect.

Formation and movement of matalapaineinen systems can occur in different meteorological contexts. Extratropical cyclones and frontal systems frequently develop as low-pressure areas in mid-latitudes, moving with prevailing wind patterns. Tropical cyclones also feature a central low-pressure area. In Finland and other Nordic regions, recurring low-pressure systems from the Atlantic commonly bring unsettled weather, including rain, wind, and changes in temperature.

In weather forecasting and reporting, matalapaineinen is used to describe conditions likely to produce unstable weather. The term also appears in everyday language to denote periods with lower atmospheric pressure and associated weather changes.