Under the Köppen climate classification, Saint Petersburg is classified as Dfb, a humid continental climate. The distinct moderating influence of Baltic Sea cyclones results in warm, humid and short summers and long, moderately cold wet winters. The climate of Saint Petersburg is close to that of Helsinki, although colder in winter and warmer in summer because of its more eastern location.
The average maximum temperature in July is 23 °C (73 °F), and the average minimum temperature in February is −8.5 °C (16.7 °F); an extreme temperature of 37.1 °C (98.8 °F) occurred during the 2010 Northern Hemisphere summer heat wave. A winter minimum of −35.9 °C (−32.6 °F) was recorded in 1883. The average annual temperature is 5.8 °C (42.4 °F). The Neva River within the city limits usually freezes up in November–December and break-up occurs in April. From December to March there are 118 days average with snow cover, which reaches an average snow depth of 19 cm (7.5 in) by February. The frost-free period in the city lasts on average for about 135 days. Despite St. Petersburg’s northern location, its winters are warmer than Moscow’s due to the Gulf of Finland and some Gulf Stream influence from Scandinavian winds that can bring temperature slightly above freezing. The city also has a slightly warmer climate than its suburbs. Weather conditions are quite variable all year round.
Average annual precipitation varies across the city, averaging 660 mm (26 in) per year and reaching maximum in late summer. Soil moisture is almost always high because of lower evapotranspiration due to the cool climate. Air humidity is 78% on average, and there are, on average, 165 overcast days per year.