Airfares have been remarkably cheap of late, but let's not live in a fool's paradise. Summer is afoot, and prices will inevitably go higher than they are now.

STA Travel, a big travel agency chain specializing in student and discount travel, is warning travelers that if there's somewhere they want to go cheaply, they'd better do it now, because prices are going up starting June 1. The current deals aren't sticking around, so to nab a trip at the low prices, you'd better go and come back by the last day of May.

"After June 1, customers can expect to see prices increase by a few hundred dollars," said its marketing manager, Robert Sessions, on the company blog. "There will still be deals, but not the steals we are seeing now."

Is it self-serving for a company that sells air tickets to tell you that you'd better buy some air tickets now? Absolutely. But it's also true.

Rick Seaney, who covers airline pricing like it was his job or something (because it is), puts the June 1 deadline in more convoluted terms: "More filled seats means more airline control over prices, and when airline control the prices, they only go one way -- up." Seaney's really saying what Sessions is: Summer travel makes prices rise. Seaney goes another step further and suggests you buy your summer air tickets now, too, regardless of whether you plan to be home by June 1.

There's a silver lining in those clouds, though. Experts are saying that because the airlines cut capacity by some 10% last fall, more flights will land on time this summer.