Analysing terrain data
The exposure grade does not take into account objective hazards (stone fall, seracs, etc) but only the consequences of falling.
Low Exposure (E1): Exposure is limited to that of the slope itself. Getting hurt is still likely if the slope is steep and/or the snow is hard.
Medium Exposure (E2): As well as the slope itself, there are some obstacles (such as rock outcrops) which could aggravate injury.
High Exposure (E3): In case of a fall, death is highly likely.
Extreme Exposure (E4): Certain death in the case of a fall.
If you get the chance to ski the middle line down East Castle then you are very lucky; it's one of the best runs at Alta and rarely open.
Get playful with jumps and cliffs or rip high speed turns down the open face.
If it's open, it is well worth the hike.