MSHC circumnavigation ski tour departing from Timberline at 12:30pm, skiing Lower Zigzag Glacier (8250’) thru MSHC Skiers-left gully to 6250’ at 3:30, skinning up Climbers-left gully and then traversing across MSHC to 8K’ above descent gully starting at 4:30 and then ski traversing Lower Zigzag Glacier back to Timberline ski area arriving back at parking lot at 8pm.
Weather-wise, a calm and chilly bluebird day turned westerly gusty at dusk. Evening winds accompanied increasing fogginess and very light precipitation thereby creating a (decreasingly) intermittant whiteout for a tech (headlamp, compass and gps-enabled topographic map app)-assisted exit.
Snow surface - a wind-defined mixed bag depending on location - seemed stable, but still took care to minimize exposure to concerning slopes underfoot or overhead, especially the former per the predominant wind slab risk, and keep in mind consequential terrain below me (secondary cliff bands below MSHC) and while skiing escape routes.
Once the sun set and accompanying fog-based whiteout set in, the predominant concern in the complicated terrain ascending and traversing above MSHC was proper routefinding. Using a gps-enabed topographic mapping app on my phone (briefly to keep it elements-functional) to obtain a bearing toward previously marked waypoints and then following that bearing via a physical compass held constantly in front of me proved to be most effective. When I deviated from this strategy, I sometimes sharply deviated from the goal shortly thereafter. East-facing failure was also noted inside Timberline ski area at the end.
Note: Having explored and topo-studied the MSHC area a bit previously, I was less concerned about major terrain traps as long as I stayed well above the cliff band. That said, especially w wind activity, small localized features - still capable of delivering a minor but very problematic injury given timing of return - required cautious movement to avoid.