From Torsten Slok:
More and more clients bring up the Atlanta Fed’s real-time tracking estimate of GDP and it has become a benchmark for discussions of current quarter GDP after they did a great job capturing the low GDP number that came out for 2015Q1, see chart below. The average absolute forecast error since they started in 2011 has been 0.7 percentage points (with an RMSE of 0.9). Their latest forecast for 2015Q2 GDP is 0.8%, see also here: Federal Reserve Bank of Atlanta