Two mountain ranges and two broad valleys make up the setting for Bulgaria's four-season climate. The Balkans run east–west through the nation's heart, and they shield the southern lowlands somewhat from outbreaks of winter cold. Along the southern border, the Rhodope Mountains help prevent the hot, humid air of Greece from sweeping northward. It's still warm here in the summer, with a big temperature jump on sunny afternoons (followed every few days by a thunderstorm). Sofia is a few degrees cooler than the low valleys to its east. Autumn brings moderate temperatures and the driest weather of the year, while winter is usually chilly and cloudy, with light snows likely at Sofia and other higher points. Late spring is the wettest season across much of the country. Along the breezy Black Sea coast, rain and snow are fairly light but well distributed throughout the year.