Begin by crossing the lake spillway and walking on the west side of the lake. A fisherman's trail of sorts follows along the west shore, climbing over fallen trees, roots, rocks and going up sometimes and dropping down other times. It’s sort of slow going. Near the north end of the lake, an opening in the forest to your left affords an opportunity to depart the now fainter trail and ascend steeply (Class 2) for a while until you clear the trees. The goal is to gain the broad ridge that leads to the unranked "Glacier Peak." Higher up, the slope will begin to relent a little and you can hike through tall grasses and tundra. Keep an eye out for a beautiful hawk that flies in this area. The hiking becomes easy Class 1 and you will make rapid progress over mostly tundra to near the summit of Glacier Peak. Here, you intersect the Continental Divide trail and continue hiking now north and then east over more easy Class 1 tundra toward the summit of Whale. In the fall, the tundra up here is quite colorful. There's a medium-sized rock cairn marking the high point of the broad, mostly tundra and embedded rock summit. It took us just a little over two hours from Jefferson Lake. While taking our lunch on this summit, we were visited by a friendly group of mountain goats who came up quite close to us. Two yearling goats played on the summit cairn, clambering up, then leaping off to clamber back up again. They tarried here for a good ten minutes while we snapped a few dozen pictures.
For the descent, try heading down the SE ridge toward Pt. 12,733. At the saddle before reaching that point, drop down SW into the Jefferson Lake Fork drainage. This fairly open valley heads south back to the north end of Jefferson Lake. This is a pleasant valley with plentiful signs of elk. At times you pass through forest but it was not difficult at all to get back to the lake. When you do reach the lake, avoid the willows at the upper end. We walked back along the east shore and followed another faint fisherman's trail that again led over various obstacles until you reach the parking area. One way mileage is 4.5 following our suggested route to the summit. If you return as suggested, you'll save about .75 mile.
Links to other information, routes & trip reports for this peak that may be helpful.