• Update – 11am Eastern
  • United Airlines Matching – Southwest’s new sale prices; Delta is also discounting on some smaller cities (not matching yet). I expect more matching at the 1pm U.S. domestic airfare distribution (hits res systems at 3pm Eastern). Keep up in realtime by following us on Twitter).

• Update – 2pm Eastern
  • All Airlines Matching Now – American, Continental, Delta, JetBlue, AirTran, Frontier and Alaska — mostly on overlapping Southwest routes. Shop Now!

It is hard to believe the “not so little low cost airline” (serving just under 70 cities now) hit its 39th year of business this month (I feel old).

True to form, Southwest which has never let any excuse for a party go to waste — has stepped up today with one of its themed airfare sales (39th Birthday Sale) that will have some lucky travelers paying under $100 roundtrip all-in for their fall trips.

I recently wrote about when to shop and buy plane tickets on Southwest Airlines and noted that Southwest typically fires off their sales late Monday night for booking on Tuesday and pulls them from their reservation system after 3-days — which exactly the case this time (sale expires midnight June 24th).

Unfortunately for those looking to purchase summer or Thanksgiving flights — this sale isn’t for you — as the travel departure window is from September 8th through November 17th (not so affectionately known as the “slow” time when kids are back in school and end of year holidays are on the horizon).

Regardless, these prices are a steal and you should be shopping today as these are likely to go fast — here are the pricing details for base airfares (excluding government and airport fees):

• $39 one way – for travel less than 450 miles (about the distance from Philadelphia to Charlotte)
• $79 one way – for travel less than 1000 miles (and more than 450 miles — about the distance from Chicago to Tampa)
• $119 one way – for travel over 1000 miles

The airline ticket steals of last years economic turmoil won’t be found this year as domestic airline sales recently have been fewer / farther between and much more restrictive — this fall airfare sale is following this restriction trend as both Friday and Sunday are blacked out — thus making prices higher on those more coveted days.

The good news is that Southwest competitors will be scrambling to match these sale prices this morning on overlapping routes which should leave a nice amount of cheap seats in reservation systems after lunch today.

We have noted recently how there has been a dearth of airline ticket sales the past several months compared to last year including the pricey summer departures with their peak travel surcharges and this sale fits right into the “airlines finally climbing out of a hole” narrative of the past few months (in May domestic airline passenger revenue was up 15% yearly and should be up another 5-10 points this summer).

That doesn’t mean you won’t be able to find a deal for summer travel — especially if your armed with insider travel tips on the best time to fly and buy airline tickets. I can’t stress enough how this year is not one you want to procrastinate on with your ticket purchases — simply put, demand is outstripping supply (for the moment), which means airlines just don’t have much incentive to discount.