U.S. airlines will carry 222 million passengers from June through August, topping the summer of 2007 when 217.6 million people flew, Airlines for America, the industry’s trade and lobbying group, predicted last week. Vacationers to Europe will fare better, with the average ticket down 3 percent to $1,619, about $50 less than last summer, according to the Airlines Reporting Corp., which processes ticket transactions for airlines and travel agencies. While airlines can plan days in advance for blizzards, it is hard to know exactly when a thunderstorm will roll through an airport, shutting down all baggage handling and flights. Add into that extremely crowded airports: 13 of the 15 busiest days to travel fall in the summer, according to the airline trade group. In July, U.S.