Tim:
Having logged about 450 miles on the Whitney Trail in the last 30 something years and been caught in numerous unexpected storms,I've gotten REAL weather savvy to save my skin.
I've noticed a phenomnenon that happens in the dawn light over the mountain that is a sure precursor of a storm. For want of a better term, I call it "heavy sky." Meaning even though it's crystal clear both east and west, over the Sierra ridge the blue sky has a slight tinge of grey and pink.The air literally looks thick. It's very slight,but it's there. Four times I have seen this sky on a crystal clear (we thought) morning and by 10AM the puffy baby cumulus clouds start building. By mid afternoon each time it was snowing on the other side of Trail Crest. Obviously it denotes a lot of moisture in the air. It's not scientific, but it sure has kept me out of trouble.
Also monsoon season officially starts about the middle of July when (i Read this in the paper) the water in theSea of Cortez in Mexico gets to 80 degrees. The Sea of Cortez is pretty much a straight shot down from Owens Valley and apparently the hot wet air from down there gets sucked up north.
I'm going for a chance on this Tuesday, sleeping at Outpost Camp and leaving around 2-3AM if not earlier. Snag the summit, get down before the storms.
Good luck and watch the skies!