säävaihteluilta

Säävaihteluilta is a Finnish term used to describe pronounced weather variability occurring within a single evening. It refers to conditions where temperature, precipitation, wind, cloudiness, or humidity change significantly over the course of the same evening, often contrasting with the more gradual diurnal pattern typical of the location.

In practice, säävaihteluilta can involve rapid warm-to-cold swings, sudden showers, or the development of fog or low clouds after sunset. The phenomenon is more common in regions with strong diurnal temperature contrasts, marine influence, or complex terrain, where small-scale processes such as sea breezes, valley flows, or frontal passages interact with the evening boundary layer.

Observations rely on standard meteorological measurements—hourly temperature, precipitation, wind, and cloud cover—along with high-resolution forecasts. The concept is not a formal meteorological category but a descriptive label used in media, weather blogs, and casual forecasting to highlight nights with notable evening-to-night variability. It poses forecasting and planning challenges, particularly for outdoor activities, agriculture, and energy demand management, which may benefit from short-term updates during late afternoon and evening.

Etymology: compound of sää (weather) + vaihtelu (variation) + ilta (evening).

See also: weather variability, diurnal cycle, microclimate, meteorology.