sadevöinä

Sadevöinä is a meteorological term used in Finnish-language sources to describe a sequence of nights with rainfall predominantly during nighttime and little or no rain during the day. The name combines sade (rain) and öinä (nights) to signify nocturnal precipitation. In practice, sadevöinä may be defined as a pattern where measurable rainfall occurs for consecutive nights, often with thresholds such as at least 5–10 mm per night and a duration of multiple nights, although definitions vary by region.

Occurrence and causes: Sadevöinä occur in moist climates where air masses rise at night or interact with topography. They are common in maritime temperate zones and tropical-coastal areas, and may be associated with frontal systems, low-pressure circulation, or localized nocturnal convection. Seasonal variability exists, and some studies consider climate change could influence their frequency or intensity.

Characteristics: During sadevöinä, rainfall is concentrated in night hours, with rainfall amounts that persist across several nights. Humidity remains high, and temperatures may be cooler at night due to radiational cooling. Daytime clear or light rainfall is less typical within the pattern, though not excluded.

Impacts and measurement: Impacts include strain on urban drainage and transportation, as well as changes in agricultural practices and increased dew or fog formation in the morning. Observations are often qualitative in everyday speech, while hydrological agencies may classify sadevöinä based on nightly rainfall thresholds and duration.

Terminology and use: The term is informal and varies by region, with no universally fixed definition. In scientific literature, sadevöinä may be described as a nocturnal rainfall pattern embedded within broader phenomena such as frontal rain events, tropical maritime convection, or monsoon-related rainfall.