"Our own Archdiocese grew by over 13,000 Catholics in 2010" says Archbishop Listecki at 3:12 in the 2012 Catholic Stewardship Appeal video, found here, with a caption "13,000 new Catholics in the Archdiocese".
The first question at the March 9, 2010 Milwaukee Press Club Newsmaker Luncheon with Archbishop Listecki (video Part 1) touches on the 38,000 fewer Catholics in the Archdiocese the previous year. The Q&A continues in video Part 2.
If the Archdiocesan membership declines were due to a wider trend of advancing secularism, that wouldn't explain a turnaround in 2010. So it doesn't appear that Church leaders have a handle on the decline or uptick. Still, there has been at least some effort here and there at internal evangelization. Even if the cause of a turnaround is unknown, up is better than down. (There are less categorical views on that last point.) The 2011 numbers will be of more than usual interest.