Home prices slid again in August, according to the latest index released Tuesday by Denver-based Integrated Asset Services, LLC (IAS).

The IAS360, which the company calls the industry’s “early detection” tool for home price trends, fell 0.2 percent during the summer’s final month.

Though slight, the decline marks the second down month in a row for the IAS benchmark, after a healthy 2.8 percent gain in prices during the second quarter of the year.

IAS reported that the South and West U.S. census regions weighed heaviest on the national index, with median prices slipping 0.1 percent and 1.2 percent, respectively. Prices in both the Northeast and the Midwest climbed 0.7 percent for the month.

“Ordinarily, there’s nothing ominous about a slowdown at the end of summer,” said Dave McCarthy, IAS’ president and CEO. “But these are hardly ordinary times. We know there’s a sizable inventory of bank-owned homes out there that will be listed at some point, and that could ignite a new wave of stress in the housing market.”

This shadow inventory of unlisted, unsold foreclosed properties could cause a great deal of trouble for a potential recovery. When the overhang hits the market, home prices will be pressured, particularly in markets with large numbers of foreclosures.

According to McCarthy, this hidden supply, along with the IAS360’s predictive characteristics, “may well be showing us the first signs of a second wave of downturn.”

The IAS index incorporates data from national, regional, metropolitan, and county levels, and suggests that several of the nation’s hardest-hit areas may already be feeling the strain. The index reports two of the country’s most distressed counties—San Joaquin in California (Stockton) and Lee in Florida (Fort Myers)—both of which were down nearly 50 percent from their high-water marks, falling another 7 percent in August.

Overall, the IAS360 is down 8 percent for the trailing 12 months and a full 16 percent from its high in June 2007.