The 3306m Brèche Nonne Evêque is the obvious thin couloir in the center of the picture above (made a bit more obvious by the dotted red line).
First skied by Jean-Marc Boivin on the 21 April 1984. Anselme Baud’s Mont Blanc and the Aiguilles Rouges: A Guide for Skiers states that it is 50°-55° for 500m, which puts it at a 5.4 in the toponeige rating system. As for the exposition then that again is a 4 in the toponeige ratings. We skied it from the first lift up the Aiguille. There is about 1300m of climbing from the Vallee Blanche so it is a reasonably big day out.
The first 800m of ascent was up easy angles slopes. On the way back down we didnt get back to here till it was nearly dark and skiing them in the pale evening light was a fantastic experience, there were a few rocks hidden in the snow and we got a shower of sparks whenever we clipped one. We then had to climb a short section of grade 3 ice at the bottom of the couloir for about 40 meters.
After the small ice section we were in the couloir proper and just had to plod up the next 500m of 50 degree snow. At times it was a bit thin with ice visible underneath, we planned our descent around these obstacles as we went up.
We got to the breche at 16:00 after catching the 08:15 Aiguille du Midi cable car. Looking over at the Droites the west face was looking in good condition to be skiied.
We didnt hang around long before heading off back down again.
At the bottom of the couloir we downclimbed the short ice section again before cruising back down to Chamonix, getting back after dark but before the bars had shut.