Apparel retailers blamed warm November weather for lackluster sales, saying it kept customers from buying sweaters and scarves, but they won’t have that excuse in December.

In fact, the weather is expected to be just cold enough to prompt sweater purchases, but not so frigid that shoppers will avoid their holiday shopping.

According to Weather Trends International, which forecasts temperatures and conditions for U.S. retailers, December is expected to bring average temperatures of about 35 degrees, cold enough to prompt those sweater sales, and mostly free of blizzards — which keep shoppers home.

“It’s going to be a milder December,” said Weather Trends Chief Executive Bill Kirk. “Not too hot, not too cold. Last year we had really cold weather and blizzards that killed store traffic. It’s all about store traffic.”

But beware of a Christmas weekend storm which will snarl traffic and keep consumers by their fireplaces, he said.

“Later December, around the 24th, the bottom may fall out,” Kirk said. “We’re advising clients to not expect that last week of December to be great (for sales).”

He said the last month of 2005 was notable for clear skies, allowing shoppers to run out to exchange items and use their gift cards. This year, it’s likely to be a different.

“We have the whole country pretty much in a deep freeze by late December through mid-January,” he said.

So, hang in there. This is coming.