pakkasjakso

Pakkasjakso is a period of several days during which temperatures remain below freezing. The term is used in Finnish meteorology and media to describe notably cold spells, typically occurring in winter. The exact duration and temperature threshold vary by region and organization, but it generally refers to consecutive days with sub-freezing temperatures.

Causes and dynamics: Pakkasjaksot often arise when a high-pressure system over the Arctic or northern Europe channels cold air southward. Clear skies and long nights promote radiational cooling, and snow cover can enhance the cooling effect, reinforcing the cold spell. They can follow milder spells or be part of the normal winter pattern.

Characteristics and effects: Colder nights give frost; daytime temperatures may stay far below freezing. Wind can intensify wind chill. In Finland, pakkasjaksot increase heating demand, raise energy costs, and affect transport, road safety, and infrastructure. Frost can damage crops, water pipes may freeze, and outdoor activities are constrained.

Forecasting and adaptation: Forecasts track expected temperatures and duration; meteorological services issue advisories when cold spells meet defined thresholds. In Finland, the Finnish Meteorological Institute monitors conditions and provides guidance on precautions, such as insulating pipes, winterizing vehicles, and preparing for icy roads.