Meteorologist Markus Mäntykannas writes in Foreca's blog that in the future, autumns can be replaced by winters, and after thermal autumn, spring can come.
Thermal autumn can be known for up to six months.
- Huh, I still remember last winter as yesterday.
That perpetual expectation from November to March: when a decent winter really begins, when this graying ends, he recalls.
Last year, the thermal winter in the south lasted only five days in some places and did not begin until the last days of February.
In winter 2007–2008, the thermal winter lasted nine days.
In thermal autumn, the average daily temperature remains on the plus side. Photo: Tatu Lertola / IS
Thermal autumn begins when the average daily temperature drops more permanently below +10 degrees.
Thermal winter is considered to begin when the average temperature drops more permanently below zero degrees.
The astronomical or astronomical winter begins with the stagnation of the winter day on December 21 and continues until the stagnation of the spring day in March.
The Finnish Meteorological Institute has previously announced the beginning of the thermal seasons by region, but the Department has decided to report the change of seasons in the future only when the dates of the whole country can be ascertained.
For example, autumn and winter start in Sodankylä on average a month earlier than in Turku.
In November 2019, it was already snowing in Helsinki at the beginning of the month, and the electric kickboards were covered in white in the city center.
However, there was no permanent snow cover in the capital. Photo: Antti Hämäläinen / IS
In the future, non-existent or few-day thermal winters may be common, with thermal autumn extending from September to October to March to April.
Meteorologists are struggling to wonder when thermal spring will begin if the winter temperature cycle is exhausted.
- So far, we in Finland have not considered how the absence of thermal winter is recorded in the statistics and at what stage the thermal autumn is considered to have changed to spring if winter is interrupted, Mäntykannas writes.
In Sweden, it has been decided that spring will begin on 15 February if the definition of thermal winter has not been met by then.
According to ECMWF, the European Center for Medium-Range Weather Forecasts will be warmer than usual in Finland from October to December.
Central and northern Finland is forecast to be 1–2 degrees warmer than usual and to the south 0.5–1 degrees warmer.
The subsequent winter months also look warmer than usual in the forecast, but forecasting the weather for months is difficult, especially in northern latitudes.
Warmer average temperatures also do not eliminate the possibility of cold periods.
According to Mäntykannas, climate change has changed Finnish winters in a much warmer direction.
In the second half of the century, according to him, the thermal winter may be interrupted more often than every third winter on the southwest coast, for example in Turku.
At the same time, summers are getting longer, so thermal autumn can only begin in southern Finland in October, when previously temperatures dropped to the autumn side, typically during September.