As airlines keep shrinking capacity, holiday travelers may find sharply limited space and higher fares on less-popular routes, said Dean Headley, an associate professor of marketing at Wichita State University and expert on airline performance. Best advice: Book now.

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Thanksgiving airline seats and fares are disappearing faster than Aunt Vera's green bean casserole.

So unless you want the leftovers, book now.

"Of course, there will be last-minute sales, but you'll only get the middle seats on the 6 a.m. connecting flight, rather than a nice seat on an 11 a.m. nonstop," said George Hobica, founder of AirfareWatchdog.com, which tracks fare trends. "If you only care about price, then sometimes it pays to wait to buy."

With seven weeks until Thanksgiving Day, Nov. 22, airfares for the holiday are up 2.9 percent nationwide, according to Priceline analyst Brian Ek. Thanksgiving airfares to and from Detroit are averaging $362 round-trip.

But some routes cost more -- much more.

Examples? If you need to fly on the Wednesday before Thanksgiving and fly back the Sunday after, you'll pay $559 round-trip from Detroit to New York LaGuardia and $572 from Detroit to Seattle.

That's more than $2,200 round-trip for a family of four.

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Lower fares out there

As airlines keep shrinking capacity, holiday travelers may find sharply limited space and higher fares on less-popular routes, said Dean Headley, an associate professor of marketing at Wichita State University and expert on airline performance.

"It's hard to say what an individual traveler might bump into, but if you are going from a large market to a large market, you should find plenty of availability," he said. "The thing that folks from the smaller markets have to know is, in order to get the prices of the past, you have to go from point A to points B and B1 and C. If you make two stops, you can still get that price you may have seen two or three years ago."

Booking early gives families a greater chance of finding seats together. And being flexible on flight days can mean lower prices.

According to Travelzoo, the cheapest days to fly will be Nov. 13-16, 22-23 and 28-29. The priciest will be Nov. 21 and 24-25.

That Detroit-New York nonstop flight falls to $327 if you fly home the Monday after Thanksgiving instead of Sunday. Detroit-Seattle is $454 if you stay a week, according to Orbitz.

One trend Ek notices is that Priceline's "Name Your Own Price" blind-bidding feature is selling Thanksgiving airfares at 20 percent off, a better discount than last year. That indicates that airlines are moving some seats through alternate channels to people who are most flexible on routes and airlines, he said. Passengers name a price and see whether any airline accepts it.

Factors to keep in mind

Travelers should pay close attention to baggage fees, which can add hundreds of dollars to the cost of flying.

Checked bags are still free on Southwest Airlines, and if you are a Delta SkyMiles American Express cardholder, the first checked bag for each person in your party is free on Delta.

However, two airlines, Spirit and Allegiant, now charge for both checked and carry-on bags.

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The nation's airlines performed well last Thanksgiving, with an 85.7 percent on-time record for peak days, except for the Tuesday before Thanksgiving, which was 78 percent on time, according to federal transportation data. Thanksgiving Day was quiet, with 26 percent fewer flights than on a normal Thursday.

This year? With airline consolidation, labor problems at American Airlines and unpredictable November weather, it's anybody's guess.

"As an industry, things went relatively well last holiday season," Headley said. "That doesn't mean if something goes wacky with the weather this year, you aren't going to get a disaster on your hands."

So, what about traveling at Christmas?

Santa may know whether you have been good or bad this year, but even he can't predict Christmas airfares.

"Airline mergers and flight cutbacks have reduced the number of seats available for holiday travel. That lessens the likelihood of fare drops," said Brian Ek, analyst for Priceline.

The national average fare for flying during the Christmas holidays will be $430 round-trip, up from $420 last year nationwide; in and out of Detroit, fares will average $396, Ek said.

Oddly, in the last couple of years, some holiday fares actually dropped as Christmas came closer, signaling weak demand or added capacity. That could happen again. Or not.

The cheapest days to fly will be Dec. 17-18 and 25 and Jan. 1, with the next lowest prices on Dec.15-16, 19, 23-24, 27 and 31 and Jan. 2, Ek said.

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