Petersburg is classified as Dfb, a humid continental climate. Distinct moderating influence of the Baltic Seacyclones result in warm, humid and short summers and long, cold wet winters.
The average daily temperature in July is +22 �C (72 �F); a maximum temperature of +37 �C (99 �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 +5.4 �C(41.72 �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 123 days average with snow cover, which reaches the average of 24 centimeters (9.4 in) by February. The frost-free period in the city lasts on average for about 135 days. The city has a climate slightly warmer than its suburbs. Weather conditions are quite variable all year round.
Average annual precipitation varies across the city, averaging 600 millimeters (24 in) per year and reaching maximum in late summer. Soil moisture is almost always high because of lower evapo transpiration due to the cool climate. Air humidity is 78% on average, while overcast is 165 days a year on average
