Snowpack gets a "D"

Rare chance to see our backcountry snowpack tested with more than body weight today. It didn't flunk. But it didn't hold up well. 

CliffNotes: The snowpack is still failing near the Jan. 13 crust, and the failures are propagating long distances and producing very large avalanches. Yet not every slope will fail under a rider's weight. Slopes less than 35 degrees seem to be releasing less regularly.

• Three of the six avalanche paths tested with explosives released very large avalanches. The three paths released with the first charge (1163, Shed 9, Shed 7 East, in avalanche tab)
• The other slopes (Infinity, Shed 8, and Shed 7 West) did not produce slides after one or more tests. 
• The tested start zones faced east to south-southeast;  they ranged from 6100 to 7000 feet elevation with one exception (5200 ft). All were generally top- or cross-loaded by prevailing winds.
• Debris from the slides ran 1700-2700 vertical feet, almost reaching or crossing the railroad grade in each instance. One powder cloud crossed Highway 2.
• The crowns were an estimated 4-6 feet deep. The crown from Tuesday's natural avalanche in Shed 7 West (avalanche tab) was up to 15 feet deep.
• We did not see avalanches on most terrain visible from the road, with the exception of a large natural slide on a southwest-facing slope on Rampage Mountain in GNP (in avalanche tab).

This combination - very large triggered slides, tested slopes with no results, and little natural activity - leaves us in a difficult, disturbing scenario. It's particulary disturbing because these start zones are unlikely to harbor the late January surface hoar. These slides likely failed on facets above or below the 1/13 crust. Which means the persistent slab avalanche problem is serious on all aspects above about 5500 feet. 

The implication for backcountry riders is pretty clear: hit the wrong spot on a slope, and it'll trigger a terrifyingly large, likely unsurvivable avalanche. Miss those spots, and you'll wonder what all the worry and fretting is about. Since we don't have x-ray goggles and can't see those spots, sticking to low angle slopes (less than 30 degrees. 30*!! not 35*) is the only way to ensure we don't release a slide even if we do collapse and crack a slab.

Oh, and more snow and wind are on the way. This hazard will linger for awhile.