We had be skiing north aspects on Sunday and Monday with great results and took a rest day Tuesday. We only expected moderate wind and that sheltered north aspects would still have good stable snow. Nothing notable or unusual was observed on our approach up the phantom and through cave ridge vicinity traversing towards Lundin. At the top of lundins north couloir, I cut a body size chunk out of the cornice and dropped it directly above where I entered. I had been getting a lot of first tracks so I offered to my partner to go first. He entered cautiously about 15 feet west, skiers left entrance. Upon dropping, his bases immediately froze and collected snow and had a controlled fall for about 20 ft. He was fine but said he was unable to move and needed to scrape his skis. We both discussed if he could move to a safe spot, he was close to the skiers right rock wall, but he was committed to scraping his skis. the snow was incredibly hard to scrape off so this whole process had been going on for 5-10minutes since he entered. I was impatient and wanted to help him, and we were both confident that the slope was stable, having survived the cornice drop and my partner skiing down and his small fall shock loading it. I told him to watch me as I entered, I skied sideways across the cornice entrance I cut, towards my partners tracks. The lip drop was maybe 1 foot coming from the side through the cut. As I reached his tracks, the slab above him (the one the cornice landed directly on) released. For reference we both weigh approx the same. He started getting carried, and I noticed my bases had froze too and I was unable to ski as fast as I normally do, about 1/3 the rate of descent. He got pulled around the corner and I yelled that I got him and started skiing as fast as I could. I grabbed his pole while heading down and observed the slide stop, total run length was 500ft. I saw him while rapidly descending and yelled out to him and he clearly stated he was ok. I ended up reaching him in about 1 min 30, down a slope that in good snow and non frozen bases would have taken no more than 30 seconds. The initial 15x15 wind pocket slab didn't propagate, and instead slid over wind board surface the whole way down carrying my partner. It was at max 12in in depth but the majority was under 6inches. The minimal amount of overall snow is likely why he wasn't buried and was able to stay on top of the slide. We found his skis, booted out and then traverse back towards the phantom. The south faces, despite cold temps, also started point releasing and felt saturated to the touch, elevation approx 5000ft, the snow was very variable based on micro terrain.
Overall looking back, despite having a "good" result from the cornice drop, we could have rapped in and dug or shocked the slope before commiting. I also could have either waited for my partner to finish scraping by himself, or make him move just a little further into a safe zone. But due to overconfidence from the slope results so far, and impatience and wanting to help him with his skis, I did not. Planning wise, i don't think we made any errors, we were planning on ski terrain and aspects and elevation we had been familiar with throughout the week (slot snot crooked, various slopes facing the middle fork etc). The wind was forecasted to blow west to east, and per alpy reports was under 20mph. We suspect that the middle fork funneled the winds to blow directly north to south and observed cornices facing the opposite direction that confirmed this. We also suspect that the winds were considerably higher than what alpy saw because it was shielded by the whole snoq, lundin, red group. Despite skiing many high danger avy forecasted days this season, this was easily the most touchy and consequential day I have been out mainly due to high level of snow variability based on micro terrain, and likely much stronger winds than were expected.