Northern San Juan

Avalanche

Robert Shuman · Mar 7, 2015 · Northern San Juan

Weather

Clear and -5 f at 6am at 10,650 ft. Light breeze. Stayed clear all day. Sun hit valley bottom around 10:30 to 11 am. Wind picked up to ~5 mph in the afternoon. Temps most likely topped out around 28 f in the shade. Sunny areas felt closer to 36 f.

Snowpack

Areas exposed to the east and not protected by other mountains or trees showed heavy wind scouring, almost to the ground in places. West facing slopes had approx. 22 inches of powder on top of a very weak layer that easily broke under trekking poles with snow baskets. Most areas had approx. 4 feet of snow under that weak layer. Limited cracking while skinning up or skiing out. Around 12:30 we started to cause large whoomphing while skinning. On slopes above 20 degrees we caused whoomphs that spread up to 60 feet uphill and 40 feet to either side every 5 minutes or less while skinning. All whoomphs were accompinied by a noticeable drop of approx. 1 to 2 inches in the snow and took place in heavily treed areas.

Avalanche

Saw a somewhat recent avalanche on a 40 to 45 degree western facing slope on the way in. 1 to 2 feet deep, 200 feet wide, Bent arm thick trees, but did not take out any larger. Slide went for ~200 yards and didn't reach valley floor. On the On the way out there was a new avalanche on either side of the previous one. Both started in the trees and were of natural causes. The northern of the two new avalnches started at about 5 meters wide and spread to about 30 meters, Continued through moderately dense trees on 35% slope. Bent wrist thick trees, no damage to larger trees noticeable. Approx. 1 to 2 feet thick. Stopped before valley floor The southern of the two new avalanches started at 25 meteres wide and 1 to 2 feet thick. It spread to approx 60 meters wide and bent trees up to arm thick. Ran for approx. 300 meters before stopping. Didn't see any sign of avalanche on Western facing slopes. 25% slope with no trees held a moose crossing it mid day.