A high pressure front moving into Finland from the south on Wednesday will cause temperatures to rise to 20 degrees Celsius and even above across much of the country over the coming days.
The unseasonal high temperatures are expected to extend as far as the southern tip of Lapland, according to Yle meteorologist Seija Paasonen, but there remains a question mark over how much the sun’s rays can penetrate the cloud formations also forecast in many areas.
"It may be that in the south clouds will dissipate and the sun will be seen," Paasonen said, adding that the humid conditions are expected to also bring rain and thunderstorms to the south and south west.
While the rest of the country basks in the unexpected September heat, temperatures in the northernmost part of the country are likely to fall to as low as five degrees Celsius, with sleet and even snowfall likely in some areas.
"We have seen from camera images in recent days that Saana [a fell in northern Lapland] has been covered with a thin layer of snow at times," Paasonen added.
Warmer start to autumn becoming the norm
In recent years, Finland has experienced warmer temperatures during the month of September, Paasonen said.
The last time there was a colder-than-average September was in 2008.
The trend this year is expected to continue into October, with the longer-term forecast indicating that temperatures will be above average in both the north and the south.
"Of course, the maximum temperatures will lower than during these coming days, but in Helsinki, for example, temperatures can rise to 15 degrees at best, while in Sodankylä the highest temperatures seem to be about 10 degrees," Paasonen said of the forecast for the beginning of October.