Cool summer didn’t favour the growing season

In Finland the past summer was chilly. The accumulated growing degree day sum, which is used to keep an eye on the growing season, was 1324 by the beginning of October. In average, the sum reaches 1433 by October. In Sodankylä, in the North, the sum was a bit closer to the normal but lower than the long-time average as well.

In the past summer, high-pressure weather conditions and heat waves have been a distant dream throughout the whole Finland. The summer has been unusually cool in the southern and central parts of the country. The cool weather has also affected the growing season conditions and the growing season has indeed fallen behind of its normal level. In the end of the summer the status of the growing season has been close to the average only in a few spots in the Lapland and south-west coast.

What about the numbers then? In the Kaisaniemi measurement station the accumulated growing degree day sum has reached 1324 by 3rd of October, whereas the average of 1981–2010 period until this date is 1433. Jyväskylä measurement station has reached a growing degree day sum of 1018 this summer, while the average number for this location would be 1170. In Sodankylä, in the very North of Finland, the growing degree day sum was 761 in comparison to the average value of 797 . Therefore, the growing degree day sum is closest to the normal in Sodankylä and the lowest in Jyväskylä when compared to the average conditions of those locations.

A similar trend was visible in the Six week forecast product of the CLIPS project. The Growing season outlook has indicated the growing season to be late throughout the summer.

When does the growing season end?

In the autumn, the thermal growing season ends when the average daily temperature sinks below +5 degrees or there is a lasting snow cover on the ground. Often severely cold night temperatures, meaning dropping well below zero several nights in a row, also mean the ending of the growing season. Officially, the end of the growing season is always defined afterwards based on the observations.

Forecasts indicates the accumulation of growing degree day sum to stall

This summer CLIPS project and its test users have tried out a new forecast product that estimates the development of the growing degree day sum in the upcoming 3-6 weeks. At the moment, the forecast product indicates that the growing degree day sum will not grow significantly in the coming six weeks in any part of Finland. If the growth of the growing degree day sum stalls in certain area for 10 days, meaning the daily average temperature stays below +5 degrees, the growing season is seen to have ended. Still, it is too early to predict the exact time for the ending of the growing season, as it is determined afterwards.