Ice accretion warnings are issued during the winter season. Ice may accrete from sea water splashes, freezing rain or fog. Ice accretion warnings are issued for moderate and rapid icing.
Yellow colour used in ice accretion warning.
The air temperature must be at -2° C or under it to cause freezing splashes in salty sea water. The surface temperature of sea water must be under +5° C. The stronger the wind, the higher the waves, and the more easily splashes are formed. Very humid air makes the situation worse. Similarly, rain or fog accompanying humid air accelerates the accretion of ice.
If the ship is sailing before the wind, ice accretion is considerably slower than if the ship is travelling at high speed against the wind.
Observation-based information on ice accretion caused by splashing is important because there are no instruments measuring the phenomenon.
The Finnish Meteorological Institute collects information on ice accretion caused by splashing. The information is entered in the FMI database from where it is immediately transferred to meteorologists' workstations. The meteorologists can use the information when preparing warnings.
FMI has produced an electronic form (link to a non-FMI website) on which the observations can be sent.