Finland is preparing for its first major thunderstorm outbreak of the year as warm and humid air moves across the country and temperatures climb above 25°C in parts of the east and southeast.
Forecasters warned that thousands of lightning strikes, strong wind gusts and heavy rain are expected between Tuesday and Thursday.
Meteorologists said the unstable weather system is developing as a low-pressure area moves north from the Black Sea region toward the Baltics.
Warm and moist air from southeastern Europe is spreading into Finland ahead of the system.
The Finnish Meteorological Institute said temperatures could break the heatwave threshold for the first time this year on Tuesday in parts of eastern Finland and more widely on Wednesday.
A heatwave day in Finland is recorded when temperatures reach at least 25.1°C at one weather station.
Oskari Rockas, duty meteorologist at the Finnish Meteorological Institute, said eastern Finland is expected to see the highest temperatures.
“The weather is warmest in eastern Finland, where temperatures are forecast to rise above the heatwave threshold for the first time this year in some places already on Tuesday and more widely on Wednesday,” Rockas said.
Foreca meteorologist Markus Mäntykannas said the combination of heat and moisture creates favourable conditions for severe thunderstorms.
The strongest storms are forecast to develop in southern and central Finland on Tuesday before shifting toward eastern and northern areas on Wednesday.
Meteorologists warned that some thunderstorms could produce damaging wind gusts, heavy downpours and hail.
On Wednesday afternoon and evening, the highest risk areas are expected to stretch from South Karelia through North Savo and North Karelia toward Kainuu and parts of northern Finland.
Wind gusts during the strongest storms could exceed 14 metres per second and hailstones larger than two centimetres are also possible, according to Foreca forecasts.
Heavy rain could reduce visibility on roads and increase the risk of aquaplaning.
Foreca said Finland could record more lightning strikes in a few days than the national average for the entire month of May. The country normally sees around 6,000 ground lightning strikes during the month.
The first thunderstorms could arrive on the southern coast during the early hours of Tuesday before spreading inland during the morning and afternoon.
Tuesday’s temperatures are forecast to rise above 25°C in southeastern Finland, while much of the country is expected to see daytime temperatures between 15°C and 22°C.
Wednesday is expected to bring the warmest conditions. In eastern Finland temperatures could reach between 27°C and 28°C before storms develop later in the day.
The Finnish Meteorological Institute said western and northern Finland will remain cooler throughout the week, with daytime temperatures mostly between 15°C and 22°C.
The hot air mass is forecast to move east of Finland by Thursday, although scattered thunderstorms could still affect eastern parts of the country overnight and during the morning.
Forecasters said the outlook for the end of the week remains uncertain. Current forecasts suggest cooler and more unsettled weather could arrive next week, although meteorologists said conditions could still change.
Finland’s highest temperature so far this year was recorded in Mäntsälä on 2 May, when temperatures reached 23.7°C.
According to the Finnish Meteorological Institute, heatwave days in May remain uncommon in Finland. Last May recorded no heatwave days, while May 2024 saw 16.
HT