The highest day temperature in December 2025 was 40°F. The lowest night temperature was 11°F. The average values for day and night temperatures during December were 31.0°F и 31.7°F respectivly.

The average sea surface temperature in December 2025 for Lahti was 34.9°F. The maximum and minimum values were 32.2°F and 38.4°F respectively.

Most of the days in December are gloomy but you can also expect sunny days.

Precipitation total in December for Lahti is 1.8 in. It makes december one of the most rainy months of the year.

The average wind speed in December is 7.6 mph. This value is relatively stable throughout the year.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for Lahti in December is 1.2 hours.