Airfare changes with the seasons, as you might expect, with higher demand making for higher prices. What you might not expect, however, is that price changes are based not just on the season in your destination but also sometimes the season in your departure region.
The price differences become particularly pronounced when you’re traveling between hemispheres. For instance, US travelers going to Australia are going to pay much less if they travel in January than in July. Even though June is Australia’s winter and therefore low season, it’s the high season in most of the United States and more Americans are traveling so fares are generally higher.