Warnings about heavy rains pertain to rains of both short and long duration. Heavy rains causing flooding occur in Finland mainly from spring to autumn.
The heaviest rains are usually recorded in late summer, when local 24-hour precipitation readings can exceed 100 millimetres.
Separate warnings can be given for heavy rains of long duration and for downpours of short duration. However, short-duration rains are associated with quickly developing thunder clouds that are more difficult to predict than extensive rain areas.
Warnings on heavy rains are issued as much as five days in advance.