Persistent values (either high or low) along the y axis suggests multiple members (and if applicable, multiple initialization times) are producing similar results.
Variable values (both high or low) along the y axis suggests multiple members (and if applicable, multiple initialization times) are producing different results.
All else equal, persistent values along the y axis should give you more confidence in a particular result. That said, your confidence in a result should decrease---regardless of inter- and intra-run agreement---as you move right (forecast farther out in time) on the x-axis.