Steel production at local mills fell this month from exceptionally high levels in December, and officials have varying ideas why.

The drop to 470,000 tons produced during the week of Jan. 19 was down from 540,000 tons recorded the week of Jan. 5. Officials say the numbers reflect an adjustment to more normal levels, that were in the 450,000- 500,000-ton-per-week range during the same time period in 2006 and 2007.

The numbers are estimated by the American Iron and Steel Institute. Spokeswoman Nancy Gravatt said the group does not provide production figures from individual mills because it is "proprietary information."

U.S. Steel Corp, spokesman John Armstrong said there were some "planned maintenance outages" on its Gary Works blast furnaces that affected its production during those weeks.

"They were scheduled, short-term outages," he said. "Regularly scheduled maintenance outages are enough to affect production."

Paul Gipson, president of United Steelworkers Local 6787 at ArcelorMittal Burns Harbor, said the first quarter of the year usually is the weakest. He theorized the production drop could be "seasonal variations" in demand from the automobile industry.

Gipson added the mill currently is operating at maximum production levels.

The automotive industry is a major customer of the Northwest Indiana mills, which produce the high-strength, light-gauge, corrosion-resistant steel used in automobile body panels, hoods and fenders.

About 62 percent of an automobile is made of steel with different grades used in the body and chassis, depending on design and location, said Deanna Lorincz, director of communications for AISI's automotive market.

Some 20 million tons, or 19 percent, of U.S. steel shipments are to the automotive industry, Lorincz said.

To adjust its output with consumer demand, the Chicago Ford Assembly plant stopped production from Dec. 16 through Jan. 5, and also will shut production from Jan. 27 through Feb. 16.

However, no one could be reached who could comment on whether the Ford plant's production stoppages affect the local steel industry.

U.S. Steel Corp. doesn't discuss its customers, Armstrong said. ArcelorMittal couldn't be reached for comment.