Kansas City, Mo. ? It seems to happen every year. Frost forms on the windows, Christmas decorations are hauled down out of the attic, and the Kansas City Chiefs become virtually unconquerable at home.

To be sure, the Chiefs enjoy an advantage in noisy and perpetually sold-out Arrowhead Stadium at any time of year, rain or shine, hot or cold.

But they’re almost unbeatable in December.

Since 1995, the Chiefs are 18-1 at home in the year’s final month. They’re currently on a 16-0 December home streak, an especially comforting stat with Denver coming to town for a key showdown in the AFC playoff picture.

A 3:15 p.m. kickoff against the Broncos today will mark the beginning of a make-or-break five-game stretch for Kansas City against five winning teams. Three are at home against AFC opponents they’re fighting for a postseason berth.

But why the Chiefs become so all-powerful at home when Santa Claus starts showing up in the malls is a mystery even to them.

“The fans still come out in droves here, whereas they might not in other stadiums,” defensive end Eric Hicks said. “It’s still just as loud as it was in September. It gets cold here. We usually are able to run the ball and play some pretty good defense in the month of December.”

The Broncos (9-2) are coming off an overtime victory at another tough place to win. Beating Dallas on Thanksgiving Day did more than allow them to maintain a two-game lead over San Diego and Kansas City (7-4) in the AFC West, however. Playing Thursday also gave them three extra days to rest and recuperate.

Running back Tatum Bell, who missed the Dallas game, returned to practice at midweek and hoped to be ready for the Chiefs.

But Kansas City in December has been especially inhospitable over the years to the Broncos: between Dec. 1 and Dec. 31, they’re 1-14 in the Chiefs’ home stadium.

“Obviously, the crowd plays a part in it,” Denver quarterback Jake Plummer said. “They’re 16-0 in December, but I’m sure their home record is a lot better win-wise. We know it’s a challenge.

“Just because their record is 16-0 in December doesn’t mean the game’s over and they’ve won.”

Their hopes of catching up with unbeaten Indianapolis for home-field advantage throughout the AFC playoffs are fading. But with Plummer enjoying his greatest season, the Broncos have reeled off four wins in a row and bring the conference’s second-best record into town.

The Broncos seized a 17-0 first-quarter lead Sept. 26 in Denver and cruised to a 30-10 victory over the Chiefs in their first meeting this year.

But Kansas City’s a different team now. In September, it didn’t have cornerback Eric Warfield and offensive lineman John Welbourn, who were suspended. More critically, Pro Bowl left tackle Willie Roaf was out because of a hamstring injury.

But Welbourn and Warfield both are back. Plus, a defense populated by a host of newcomers seems to be coming into form. Defensive lineman Ryan Sims, who injured his foot in the season opener, might even make his long-awaited return today.

Most importantly, Roaf returned with a vengeance last week as the Chiefs beat New England, 26-16, for their third victory in four games.

“Willie Roaf, so help me God, played the ballgame as well as he’s played any game since he’s been here,” Chiefs coach Dick Vermeil said. “He was outstanding, in my opinion.”

It will be up to Roaf to keep pass-rush specialist Trevor Pryce out of quarterback Trent Green’s face, and to help blast open holes for one of the league’s hottest running backs.

Larry Johnson had 119 yards and a touchdown against the Patriots, giving him 330 yards in just his last two games, a franchise record. If he gets 100 yards against the Broncos, he’ll tie the team record with five 100-yard games in a row.

The way the Chiefs usually click at home in December, Johnson’s chances seem good.

“I don’t know how to explain it, if it’s an anomaly or not,” Hicks said of Kansas City’s December home dominance. “But we’re rolling on defense right now. The offense seems to be rolling. Special teams are coming along.

“I hope we’re 21-1 in December by the end of the year.”

Actually, 20-1 is the best he can hope for. The regular-

season finale against Cincinnati will be played Jan. 1.