U.S. home prices rose modestly in June, pushed up by strong sales and a limited supply of available properties. The Standard & Poor's CoreLogic Case-Shiller 20-city home price index, released Tuesday, increased 5.1 percent in June compared with a year ago. That's down from a 5.3 percent annual gain in May and is the slowest year-over-year pace since last August. Home values are still soaring in the Northwest, but have slowed to more sustainable rates elsewhere. In Northeastern cities such as New York and Washington, D.C., they are rising at roughly the rate of inflation, and in Boston, less than 5 percent. Still, nationwide prices are increasing more quickly than incomes as buyers compete for the dwindling supply of available homes. That could stifle sales in the coming months. Home prices in the Northwest continued to climb at a double-digit pace. They rose 12.6 percent in Portland, 11 percent in Seattle, and 9.2 percent in Denver. Those three cities have topped the list of price gains for the past five months. Cities in the Midwest were mixed. Home prices in Cleveland and Chicago rose 2.5 percent and 3.3 percent, respectively, while in Minneapolis they climbed 5.1 percent, the same as the nationwide pace. Southern cities saw stronger price gains. They rose 8.9 percent in Dallas, 7.9 percent in Tampa, and 5.8 percent in Atlanta. The 20-city price index plunged after the housing bubble started to burst in 2006, plummeting by more than a third before prices began to rise again in March 2012. In June, they were still 8.1 percent below their peak level. The Case-Shiller index covers roughly half of U.S. homes. The index measures prices compared with those in January 2000 and creates a three-month moving average. The June figures are the latest available.