New climate normal period 1991-2020 is taken into use
The Finnish Meteorological Institute is introducing the new normal period at the beginning of October. Normal periods are periods of 30 years in which calculated statistics describe, among other things, weather averages and variation ranges in the recent past.
Statistics have been calculated based on weather observations from 1991-2020, with whose help the present weather can be placed in its historical context, for example by making comparisons to see if the past month was colder or warmer than usual. In addition, statistics can be used for anticipating what the weather is most likely to be like at a certain time of the year, or what kinds of conditions people should prepare for.
“Weather conditions vary from one year to the next. The weather conditions of an individual year do not give an accurate image of the climate of a specific locality, for example. To get that, we need to examine longer-term averages”, says meteorologist Pauli Jokinen at the Finnish Meteorological Institute.
The 30-year period covered by the normal period is long enough for exceptional weather conditions in a single year not to significantly affect the average, but it is also short enough for the climate not to undergo significant changes in the period.
For the first time the Finnish Meteorological Institute has produced both weather statistics as well as marine statistics from the same period. The marine statistics now being calculated include sea level height and sea surface temperatures as well as the area covered by sea ice.
Normal periods also reveal advance of climate change
The mean temperature of Finland in the new normal period is about 2.9 °C which is about 0.6 degrees warmer than in the previous one, from 1981-2010. Compared with the 1961-1990 period the average temperature has already risen by about 1.3 degrees. The greatest change has been in December, and the smallest has been in June and October.
The annual precipitation in Finland with the new normal period is approximately 609 mm. The amount has increased by about two percent from the previous period, 1981-2010, and by about nine percent from the 1961-1990 period. Growth has been greatest in the winter months, from December to February. In August, precipitation has decreased.
“The changes that have been observed between normal periods are especially underscored when we look at winters in the south. The length of the thermal winter has decreased in the southwest of the country by more than two weeks compared with the previous normal period ten years ago”, Pauli Jokinen says.
The duration of the permanent snow cover has decreased in southern and central parts of the country by 1-2 weeks, and even more in areas near the coasts.
In connection with updating the normal period statistics, the definitions of some weather terms have been updated, such as the rare and exceptional weather phenomena.
The next update of the statistics of the normal period will take place in ten years, according to the instructions of the World Meteorological Organisation WMO, when observations for 2001-2030 will be introduced.
Further information:
Normal period in the online service of the Finnish Meteorological Institute (in Finnish)
Definitions of weather terms (in Finnish)
Marine statistics (in Finnish)
The climatic normal period project and climate statistics: meteorologist Pauli Jokinen, Finnish Meteorological Institute, tel. +358 50 570 2161, pauli.jokinen@fmi.fi Marine statistics: Head of Group Antti Kangas, Finnish Meteorological Institute, tel. +358 40 867 8838, antti.kangas@fmi.fi Normal period and climate change: Head of Group Antti Mäkelä, Finnish Meteorological Institute, tel. 050 301 1988, antti.makela@fmi.fi