Original sentence: Climbing incidents on Mount Hood:  all recent incidents have been caused by whiteouts.In less extreme cases, it may suffice to break the snow surface by throwing a snowball ahead.It is only when a contrasting object is placed on a snowy surface that the surface can be detected.Motorists, especially those on large high speed routes are also at risk.This effect is exacerbated by a smooth surface of fresh snow.Whiteout conditions pose threats to mountain climbers, skiers, aviation, and mobile ground traffic
Edited sentence: (In less extreme cases, it may suffice to break the snow surface by gently throwing a snowball ahead).(This effect is accentuated by a smooth surface of fresh-fallen snow).It is only when a dark or coloured object is placed on a snowy surface that the surface can be seen at all.Motorists, especially those on large high speed routes are also at serious risk.Whiteout conditions pose the greatest threat to aviation and mobile ground traffic operations