Economic forecasters worry the combination of a real estate market in the doldrums and unfortunate timing may be blowing in a blizzard of new foreclosure filings. The first flurries are already arriving.

December marked a tough milestone, with 1.2 million foreclosure filings reported nationwide for the year -- a 42 percent increase from 2005. While not a record high, such a sharp increase worries real estate experts that the worst may be yet to come, and the real estate market may suffer for it.

The strange thing about this wave of foreclosures, says Rick Sharga, vice president of marketing for the online foreclosure marketplace RealtyTrac, is that national economic conditions wouldn't have predicted such a sharp spike in housing troubles. As a whole, the stock market is in good shape, and employment numbers are strong.

Still, David Lereah, chief economist for the National Association of Realtors (NAR), says economists do expect foreclosures to follow a downturn in the housing market, especially in markets that see unsustainable price appreciations.

"That was expected. Everyone was already talking about how foreclosures would go up, even before those numbers came in," he says.

That's because when housing prices fall buyers head for the sidelines, and homes sit on the market longer. That spells trouble for people who might be relying on endless appreciation to bail them out of financial trouble.

"Any time you take buyers off the market, that takes one more option off the table for owners who are in trouble," Sharga says. "With a red-hot market, you usually don't have a foreclosure problem."

But with sagging prices and longer times to sale, trouble brews. For example, when homeowners who are in financial trouble try to bail themselves out by selling their home, the sale may not come in time, and in some cases, it may not throw off enough cash to solve the family's financial crunch.

"The two worst things you could have happen if you are in financial trouble is losing money or time," Sharga says.

So, to some extent, this wave of foreclosures shouldn't be raising eyebrows. But economists are making rumblings that something else might be at work driving this foreclosure storm. That's because if a slumping market were the only factor at work, filings likely wouldn't have spiked so quickly and to such heights. Observers believe that the other factor might have to do with a popular mortgage trend many homeowners have been jumping on for nearly half a decade.

In mid-2003, mortgage rates hit their lowest point in years, with 30-year fixed rate loans going for little more than 5 percent. But many buyers passed on the stability of the fixed rate and pounced on the rock-bottom rates being offered on 3/1 adjustable rate mortgages (ARMs). Those ARMs saw teaser annual interest rates of 2 percent and 3 percent and -- in cases with more exotic loans -- even less.

The trouble with ARMs is, after their introductory period, that interest rate adjusts upward to a market rate -- which is now closer to 6 percent. A 3/1 adjustable mortgage means that the introductory rate remains the same for three years. After that, it adjusts annually.