Tbilisi has a humid subtropical climate (Köppen climate classification: ''Cfa'') with considerable continental and semi-arid influences. The city experiences hot, humid summers and moderately cold winters. Like other regions of Georgia, Tbilisi receives significant rainfall throughout the year with no distinct dry period. The city's climate is influenced both by dry (Central Asian/Siberian) air masses from the east and oceanic (Atlantic/Black Sea) air masses from the west. Because the city is bounded on most sides by mountain ranges, the close proximity to large bodies of water (Black and Caspian Seas) and the fact that the Greater Caucasus Mountains Range (further to the north) blocks the intrusion of cold air masses from Russia, Tbilisi has a relatively mild microclimate compared to other cities that possess a similar climate along the same latitudes.