WASHINGTON (AP) - U.S. home prices fell for the second straight month in December as brutally cold weather, tight supply and higher costs slowed sales. The Standard & Poor's/Case-Shiller 20-city home price index declined 0.1 percent from November to December, matching the previous month's decline. The index is not adjusted for seasonal variations, so the dip partly reflects slower buying as winter weather set in. For all of 2013, however, prices rose by a healthy 13.4 percent, mostly because of big gains earlier in the year. That was the largest gain in eight years. 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 December figures are the latest available.