The latest S&P/Case-Shiller Index values, out today, show that a key measure — the 10-city composite — posted an annual decline of 2.7 percent in April, the worst reading since late 1991. From the press release:

“A review of the decline in home price returns on a regional level shows no region is immune to the weakening price returns,� says Robert J. Shiller, Chief Economist at MacroMarkets LLC. “While regional economic fundamentals may be keeping cities like Portland1, Seattle and Charlotte in positive territory, they have not curbed their diminishing returns. For example Seattle reported annual returns of 9.6% this month compared to the 17.8% reported for April last year. In addition, Miami has crossed into negative territory this month, with a 1.0% annual decline. � In other parts of the country, the state of the single-family residential market is weak with Detroit reporting a 9.3% annual decline, followed by San Diego with a 6.7% decline and Washington D.C. at -5.7%. Four cities – Atlanta, Boston, Dallas and Denver – did see both monthly price increases in April and some modest strengthening in their annual rates of return. A few more months of data will reveal if is a seasonal issue or the beginnings of a recovery in these markets.

While some might be surprised by the gains being registered, I do think we’ll see a few key markets turn the corner in the next two quarters. Boston would surprise me, but seeing Atlanta, Dallas and Denver begin to show moderated gains strikes me as reasonably likely. The 20-City Index also registered a 2.1 percent drop in the price for sales of existing single-family homes across the U.S., but nonetheless points to the current state of most major housing markets across the United States. The April figures show that 14 of 20 cities reported in the composite had prices that dropped or remained flat compared to 2006, S&P said. Update: If you haven’t read yesterday’s post on what the OFHEO thinks about the S&P indices, you should.