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.
In Hanover
How often does it happen in Hannover?
The DWD station Hannover averaged 64.6 frost days per year in 1991–2020. April still averaged 4.1. No individual year contains a fraction of a frost day; the decimal comes from averaging many years.
This station statistic does not fix the last frost date in a garden or conditions in every district. A warm afternoon is certainly no proof that the following night will stay frost-free.