A split between housing markets that enjoyed spectacular returns during the boom, and those markets -- often in America's heartland -- that did not, is becoming more apparent as the nation's mortgage crisis and housing slump drags on. A report released Tuesday by PMI Mortgage Insurance Co. said that the risk of price declines has risen in 39 of the nation's top 50 metropolitan statistical areas, while noting that many of the riskiest MSAs are geographically concentrated in California and Florida, as well as certain locales in Arizona and Nevada. Click here for the full report. Twelve of the nation's Top 50 MSAs are in PMI's highest risk rank, with a greater than 60 percent chance that home prices will be lower in two years. The riskiest include Riverside, CA (94 percent), Las Vegas (89 percent), and Phoenix (83 percent) -- markets already in the midst of signficant price corrections. Some of the least risky markets, according to the survey, are Fort Worth-Arlington, and Dallas-Plano-Irving, TX; Columbus, OH; and Kansas City. "We're seeing an increasingly polarized market," David Berson, PMI's chief economist, said. "The risk that home prices will be lower in two years has increased for many of the largest cities in the nation, although areas that saw only moderate home price gains during the 2002 to 2005 period still generally have low risks of price declines." PMI also updated its risk model this quarter to explicitly account for foreclosures and housing supply, it said. Also noteworthy in the report: PMI authored an opinion piece on when it expects housing markets to rebound; the bottom line is not soon, with PMI citing "unusual conditions in the US housing market." The mortgage insurer said "[it's] difficult to estimate when home price conditions will improve, but we think it is unlikely that house prices will turn around in 2008."