I suppose this unpredictability alone could make one argue that this shouldn't count as a legitimate waterfall. Either way, I put this page in so you can decide.

In any case, you could make the argument that this really should be called "Washburn Point Falls" because I recalled hiking across a flooded part of the Panorama Trail somewhere beneath Washburn Point. And it's totally reasonable to conclude that the cascade responsible for the flooding on the trail also drained further downslope over the cliffs carved by the Merced River at least 2000ft or more below from its brink close by the Happy Isles and its confluence with Illilouette Creek.

Directions: As mentioned earlier, you can look for this waterfall about just under a mile or so (during the uphill hiking) along the John Muir Trail between the Happy Isles Trailhead (signpost V24) and the Vernal Fall footbridge. It's also possible to see this waterfall directly from both the Vernal Fall footbridge as well as the brink of Vernal Fall.