Nattfroster

Nattfroster, or nattfrost, is the occurrence of air temperatures at or below 0 °C during the night, causing ice to form on surfaces. It is most likely on clear, calm nights when radiative cooling is strongest. Frost can appear as white frost or hoarfrost on exposed surfaces, while a “black frost” term is used in some regions for frost that forms without visible surface frost.

Formation and distribution depend on local conditions. Low nighttime temperatures are common in open, flat terrain, valleys, and near water where cold air can pool. Frost risk is higher during autumn and spring, when plants are susceptible and nights are still cool. Microclimates, vegetation cover, soil moisture, and wind influence when and where nattfrost occurs.

Impacts on vegetation and agriculture can be significant. Frost can damage buds, blossoms, and young shoots, reducing yields in fruit and vegetable crops. Gardens and nurseries may experience plant injury if frost protection measures are not used. In some cases, frost can occur after unseasonably warm days, creating misleading conditions for growers.

Prevention and mitigation strategies include monitoring forecasts and local frost advisories, using physical protection such as row covers, cloches, or plastic tunnels, and employing windbreaks or insulation around vulnerable crops. Other practices are choosing frost-tolerant varieties, delaying planting, or employing irrigation or heated enclosures in high-value crops. Proper site selection and soil management, including mulching in late autumn, can also reduce frost exposure.

Nattfrost is a regular consideration in temperate and Nordic climates. It interacts with seasonal timing and microclimates, and its occurrence is influenced by broader weather patterns and climatic variability.