(Newser) – If you're a fan of the McDonald's McRib sandwich, AdvertisingAge has some bad news for you: It won't be out until mid-December, instead of the usual late October. The reason sheds some light into the world of fast-food business sense. AdAge got its hands on a company memo explaining that McDonald's was holding back the popular sandwich to help boost the chain's sales numbers in December and into the first quarter.

Why? It seems that last winter's sales figures were so strong—up 9.8% in December, thanks mostly to the mild weather—that the company is worried about having terrible year-to-year comparisons this year. But it's not all bad news for McDonald's sandwich fans: The chain will put out a new Cheddar Bacon Onion Angus burger in the fall, and a similar one with chicken. (Read more McRib stories.)

