Pick a lake on the map or search by name. The freeze-up forecast is calculated from SYKE's hydrological model and from the weather forecast (Finnish Meteorological Institute, yr.no in Lapland) with the ice calculator and the ice predictor.
How the forecast is made
Hydrological model: ice thickness and surface water temperature computed by the Finnish Environment Institute's hydrological model (WSFS) in grid cells of about one kilometre. The model covers a week back and about a week ahead.
Ice calculator / Ice predictor: calculate ice growth hour by hour from the weather forecast. The ice calculator uses a formula based on the book Långfärdsskridsko (Finnish edition: Retkiluistelu), and the ice predictor uses the Isprediktor model, which also takes the ice thickness and snow ice into account. In the ice calculator, solar radiation is taken from the book's table by date and latitude and distributed over the hours according to the sun's elevation: there is none at night, and cloudiness reduces it. Neither predicts melting, and both assume the water is already at freezing point. A snow layer of at least 2 cm slows growth to a tenth.
The temperature chart shows observations from the nearest weather station and the surface water temperature from the nearest SYKE station on a lake of similar size (within 50 km). If there is none, the nearest lake station is used and the reason it is not comparable is given. If the models show ice although the surface water is clearly above zero, a note appears above the charts.
Basic lake data (area, depths, volume, elevation and catchment) come from the lake register of about 58,600 lakes. The search finds a lake by the beginning of its name or of any word in it, without Finnish letters (ä, ö), by a Sámi name or by lake number.
Nearby lakes: when you click the map, the app finds the lakes around the point and orders them by how early or late they are estimated to freeze. The lakes appear on the map as numbered markers: the colour shows the catchment and the border the main river basin. River basin boundaries are drawn on the map. If you click on land, the forecast is calculated for the nearest lake matching the criteria.
A lake is considered frozen when the ice is at least 1 cm thick.