Rankkasade

Rankkasade is a Finnish meteorological term describing a period of intense rainfall. It refers to rainfall of high intensity, typically with rates around 25 millimeters per hour or more, and lasting from several minutes to a few hours. The term is used to distinguish heavy, potentially disruptive downpours from lighter rain or drizzle and is often invoked during convective storm activity.

Formation is usually due to convective processes in warm, unstable air. Strong surface heating causes rising air and the development of cumulonimbus clouds, from which intense rain can be released in a short time. Rankkasade is often localized, meaning that only parts of an area experience the heaviest rainfall.

Characteristics and effects include brief but very heavy downpours that can be accompanied by thunder, lightning, hail, and gusty winds. Such events can rapidly overwhelm drainage systems, cause localized flooding or flash floods, reduce visibility, and disrupt transportation, especially in urban areas where impervious surfaces hinder infiltration.

Observation and forecasting rely on weather radar, rain gauges, and numerical models to identify areas of high rainfall intensity and to issue warnings. Rankkasade is a common feature of Finnish convective weather and is an important consideration in weather forecasting, urban planning, and risk management associated with summer storms.