Finland is heading towards colder and wetter weather after a slow start to autumn, raising the risk of icy roads across a growing part of the country. Foreca expects temperatures to fall during the coming week, while overnight frost, fog and moisture on roads are set to create more difficult conditions for drivers.
High pressure will keep conditions warm in parts of southern and western Finland for another couple of days. Temperatures could reach 17–18 °C in the south-west on Thursday and in southern and western areas on Friday, according to Foreca.
Fog and low cloud remain the main sources of uncertainty. Fog formed under light winds has persisted well into the morning in some areas and could remain into the afternoon. Where cloud persists, daytime temperatures could stay around five degrees below those in nearby sunny areas.
Conditions will start changing over the weekend as high pressure moves away. Cloud will increase and rain will spread from the west.
Foreca expects several areas of rain to cross Finland next week, with low-pressure systems moving over or close to the country. Colder air will also spread south.
Temperatures in southern Finland are expected to remain between 10 °C and 15 °C early in the week before falling to around 10 °C after midweek. In Lapland, daytime temperatures could approach zero towards the end of the week, with parts of the far north dropping below freezing.
Forecast models have also indicated the possibility of a stronger low-pressure system late next week. Foreca said such a system could bring the first substantial sleet and snowfall of the season to Lapland, although its development remains uncertain.
A growing road-ice risk
Road surfaces have so far remained above freezing across most of Finland, with sub-zero surface temperatures mainly recorded in the north. That situation is expected to change as October progresses.
Foreca meteorologist Sara Salonen said road surfaces could fall below freezing during clear, calm nights even when the measured air temperature remains one or two degrees above zero.
Bridges and grade-separated junctions pose a particular risk because their surfaces lose heat faster. Moisture close to lakes and other bodies of water also increases the conditions needed for frost formation.
Ice can form in several ways. Moisture in the air can freeze directly onto a road surface when its temperature falls below zero. The resulting thin layer of frost is sometimes difficult to see.
Freezing fog creates another hazard. Supercooled water droplets freeze when they strike cold surfaces, combining poor visibility with reduced grip.
Foreca advises drivers to reduce speed and leave more space between vehicles when visibility deteriorates. Dense fog can cut visibility to a few dozen metres, leaving drivers only seconds to react to an obstacle.
The colder outlook follows a September that was warmer than the 1991–2020 average across Finland, according to the Finnish Meteorological Institute.
The national mean temperature reached 10.3 °C, with temperatures generally 1–1.5 degrees above the long-term average. The month’s highest temperature was 21.8 °C at Kokemäki on 2 September, while Muonio recorded a low of -6.4 °C on 7 September.
September was also wetter than usual across large parts of the country. Lieksa Koli recorded rain on 27 of the month’s 30 days, the highest September total in the station’s 58-year observation record.
HT
