A very broad review of this relationship suggests that at low rates, a 1% incline is probably, for practical purposes, an inversion. We were close to this level after the rate hike in late 2015, but something pulled us back up. If the Fed had hiked earlier in 2016, that might have tipped the scales back down.
As we proceed through 2017, it will be important to watch long term rates. If they remain low or decline, and if at the same time new data on employment and inflation triggers a new rate hike from the Fed, then that will be bearish. The 10 year yield is currently about 1.8% above the Fed Funds Rate.