Press release archive: 2009

Finnish Meteorological Institute to start warning about heavy rains

26.5.2009 12:50

Examples of new warnings.

The Finnish Meteorological Institute will improve its warning system by introducing new warnings in May. Warnings related to thunderstorms, strong winds and heavy rains will make it easier than before to prepare for dangerous weather conditions and increase safety.

The new warnings are related to thunderstorm wind gusts, wind warnings in land areas and heavy rains. At the same time, to make it easier to estimate the dangerousness of weather phenomena and to prepare for dangerous weather conditions, a three-step classification is applied to these warnings. The three levels and colour coding used in these new warnings effectively link Finland to the international Meteoalarm warning system.

Two different rain warning types to be employed
As an entirely new form of warning, the Finnish Meteorological Institute will, in May, take into use heavy rain warnings. There are two warning types. One of them gives a warning about heavy, thundery rains of a short duration. There are three warnings thresholds; rainfall exceeding 20, 30, and 45 millimetres per hour.
In addition to warnings about shower type rain lasting for a short time, warnings will be given about heavy rains of a longer duration that accrue during a single twenty-four hour period. The corresponding warning thresholds are 50, 70, or 120 millimetres in twenty-four hours. There are no special warnings about snowfalls, but during winter, warnings on bad road conditions indicate a risk of heavy snowfall.

More specific warnings about thunder squalls and high winds
From the beginning of May, three-level warnings about thunderstorm wind gusts will be issued for all land areas regardless of whether the gusts occur over land or inland waters. Previously only one-level warnings related to inland waters or land areas were in use. Severe thunderstorm warnings are indicated by the warning map as follows:

* Yellow lightning bolt: Thunderstorm wind gusts over 15 m/s
* Orange lightning bolt: Thunderstorm wind gusts over 25 m/s
* Red lightning bolt: Thunderstorm wind gusts over 30 m/s

- Regarding thunderstorm wind gusts and thundery rainfalls one should remember that due to their short duration it is a very challenging task to forecast them. Summer rains can form and dissipate very fast, and there may be heavy rainfalls in a very small area, Meteorologist Ari-Juhani Punkka points out.

Previously, wind warnings for land areas were used to warn about thunderstorm wind gusts as well as about extensive strong winds related to low pressures. After the change, the role of the warnings will become clearer, the wind warning for land areas having to do with extensive low pressure winds only. The three-step structure and Meteoalarm colour codes will be taken into use in wind warnings for land areas also. In addition, the warning limits, instead of being related to average wind speed are tied to the strength of wind gusts. The warning limits are 20, 25, and 30 m/s. Wind warnings in sea areas remain unchanged.

Developments continue
The change in May will be the first part of a much more extensive change in the Finnish Meteorological Institute's warning system. During 2010 and 2011 the traditional 24 hour warning time will extend to 3 - 5 days. In addition, the warnings related to the first few hours will be stepped up for the most hazardous weather conditions. At the same time, the spectrum of the phenomena subjected to warnings will widen by warnings related to extreme temperatures, to sea level and wave height.

In addition to the new warnings practice, the Finnish Meteorological Institute will also start developing a system for providing real-time warnings of heavy rain and a system for distributing them. The provision of information will be on the basis of measurements carried out using weather radars, satellites and lightning location systems. The information will be updated as frequently as every 30 minutes for each locality in Finland and can be received on the Internet and on mobile phones. Users can set their own warning thresholds. The system, to be introduced on a trial basis in 2011, is part of the RAVAKE development project supported by Tekes and a number of Finnish companies and corporations.

More details:
Ari-Juhani Punkka, phone (09) 1929 3630,
Current warnings