just got back from mt whitney 05-06-12. here are the conditions for the entire trail:

PORTAL to LONE PINE: clear.

LONE PINE to MIRROR LAKE: patches of black ice before 5am.

MIRROR LAKE to TRAIL SIDE MEADOWS: minor patches of snow. no gear required.

TRAIL SIDE MEADOWS to TRAIL CAMP: significant amounts of snow. gear use optional.

SWITCHBACKS: inaccessible. only way is up THE CHUTE. takes about 2-3 hours. crampons, axe, poles, gaiters required.

TRAIL CREST to SUMMIT: snow and icy patches. Micro spikes + poles will help tremendously.