According to the 1981-2010 normals released by NOAA’s National Climatic Data Center (NCDC) on July 1, temperatures across the United States were on average, approximately 0.5 degree F warmer than the 1971-2000 time period.
Check out these two links that reveal the new 1981-2010 normals which indicates this U.S. average temperature increase.
Average U.S. Temperature Increase 0.5 degrees F (New 1981-2010 Normals)
New Annual Normal Temperatures for U.S. reflect Warming Trend