I was just cruising online looking to book a flight for my late-winter vacation when I noticed a disturbing occurrence: Discount airline Southwest is discontinuing its Boston-to-Philadelphia service effective February 11th.

My late-winter vaca isn’t to Philly, mind you, but I need to get to the City of Brotherly Love before I can get to Miami. And not being able to get there for 49 bucks each way is a bit disconcerting, if only because it leaves USAirways – an airline with already-too-high prices – as the only carrier providing direct service between Boston and Philadelphia.

Southwest, which only began providing the service between East Coast hubs in February of 2010, made the announcement unscrupulously, with a simple banner on their site informing passengers that service between the two airports will be stopped on just before Valentine’s Day.

Southwest spokesman Chris Mainz said Tuesday that the Philadelphia-Boston route “just hasn’t performed the way that we would have liked.”

What’s worse, the airline will also be pulling its service from Manchester, NH and Providence, RI on January 8th, effectively taking the discount market out of New England (if you still consider JetBlue to be a discount carrier, you probably don’t travel enough for this news to affect you too drastically).

Southwest is expanding its presence in Atlanta, where the recently-acquired AirTran was based, and Denver, where United Airlines is scaling back their service.

Speculation is that JetBlue – to date Boston’s largest carrier – may now try to make inroads in Philadelphia (which, having family in Philly, I’d be totally okay with), but Southwest simply wasn’t able to make money off of the route, forcing it to cancel it.

Until JetBlue can get there, however, it’s unlikely that USAirways is going to show any remorse in pricing their tickets from Boston to Philadelphia, so get those spring break tickets now while prices are low.