A forest fire warning is issued when the terrain is dry
When a forest fire warning is in force, it is forbidden to start an open fire in or near a forest.
The yellow colour is used in forest fire warnings and grass fire warnings.
A forest fire warning is usually given and cancelled at noon. The warnings are specific to each province. Municipality-specific warnings may also be given in Northern Ostrobothnia (mainly for Kuusamo, Taivalkoski and Pudasjärvi) and in Lapland.
Most often, the first forest fire warnings of the year are issued in early May. The forest fire warning season ends in September or at the latest in early October.
Forest fire warnings are issued using an index calculated by means of a model that describes moisture conditions in the top soil layer measuring about 6 centimetres in thickness. The input data for the model includes precipitation and air temperature.
The risk of grass fires exists in spring
If necessary, warnings for grass fires are issued in April–May. The previous year's dry grass is exposed from under melting snow in spring and may catch fire even if trees do not yet ignite easily. Grass fire warnings are issued no longer once the growing season has got off to a good start.
Precautions during a forest fire warning
When a forest fire warning is in force, it is forbidden to kindle an open fire in or near a forest.
Caution is also needed when handling fire during a grass fire warning.
According to current legislation, the authorities need not be notified in advance when burning, e.g. garden waste. The burning must not cause any harm or damage to neighbours. It is not allowed to make an open fire without landowners permission.
Municipal environment boards have issued municipal regulations and guidelines for burning garden waste. For instance, some municipalities have imposed a total ban on burning twigs. Controlled silvicultural burning of forest always requires the permission of the duty officer at the regional rescue department.