Witnessed a large D2 or D3 wet slab come off of Chair Peak when about to descend typical route from Snow Lake Divide. Avalanche traveled right down heavily traveled uptrack/ski route. Nobody caught in the avalanche thankfully even though multiple groups in area. Our group and another group switched beacons to search mode in case anybody caught although we were pretty sure nobody was. One person traversed debris and others skied down alongside it. Blunt reminder that late day conditions on warm days are dangerous even if the sun had been behind the clouds for a couple of hours.