The crux when I did it, crossing the bergshrund. Fun scrambling and climbing just left of the snow. One of many routes to the summit of Thunderbolt. Approach from Sam Mack Meadow and the Thunderbolt glacier. Once at the top of the couloir, it's a short scramble to the true summit.

Not sure of the sorting here. Underhill Couloir and Australian Arete are to the left of North Couloir and use the same approach from Glacier lodge.

See beta photo.

In low snow years this is a scramble. At other times you may want axe and crampons.