Frost day
Temperature & humidity
A frost day is a day when air temperature falls below 0 °C at least once. The afternoon can still become considerably warmer.
A brief frost is enough
A frost day is defined by the minimum air temperature at the standard measuring height. It must fall below 0 °C; exactly 0.0 °C is not enough. An afternoon maximum of 2 or 12 °C does not change that classification.
Frost, ice days and ground frost
An ice day has a stricter definition: even its maximum stays below freezing. Every ice day is therefore also a frost day. Ground frost differs because air close to the ground or a surface can be colder than air at two metres.
What an average count means
A long-term average may contain a decimal even though each individual frost day counts as a whole day. Read these averages together with their station and reference period. Conditions in the city centre can differ from those on the outskirts.