August in Lahti is the rainiest month of the year. In August, the weather in Lahti is typically warm. Average daily high temperature in August is about 18 degrees above zero. On average, Lahti has 21 rainy, 7 sunny, and 3 cloudy days in August. The rains are usually moderate. August as well as April, October, and November is considered the most uncomfortable time to visit Lahti.