Boston. Beginning sometime in the fall.

This is a move driven by weakness — a soft economy means that Southwest can’t fill its planes. As a result, the airline is moving capacity to where it sees opportunity. And that would be the major markets it doesn’t currently serve.

I wrote previous that Charlotte was the second or third largest market Southwest doesn’t serve, behind only Atlanta and perhaps Boston, depending upon whether you consider flying to Providence, RI and Manchester, NH as serving the Boston market. Southwest has now answered that; while Providence and Manchester were once close enough to Boston, which can be expensive to operate out of and can have capacity issues, obviously Southwest no longer feels that way.

Where does this leave Charlotte? As unambiguously the second largest market that Southwest doesn’t serve. And given that Southwest is most definitely a big-market carrier, CLT remains someplace that Southwest will eventually add. The question is when, not if.

Oddly, a continued weak economy may provide CLT’s best chance of landing some LUV sooner rather than later. If Southwest finds six months from now that it still has some extra airplanes that it’s looking for something to do with, Charlotte would remain a strong possibility. However, once the economy picks up, that opportunity disappears. So it could be 2010 for CLT or if not, not till maybe 2013 or 2014.

Bonus observation: The major markets Southwest still doesn’t serve (aside from the obviously not happening like ORD, DFW, and IAH): Atlanta, Charlotte, Cincinnati, Memphis, Milwaukee.

Major airports not served in markets Southwest is in: Newark, JFK, Washington Reagan National, Miami

All these have some sort of issue. Southwest picked all the low-hanging fruit a long time ago, and their moves the last few years show they’re willing to operate from airports that are expensive operate out of, are delay-prone, or are someone else’s hub.