Southern San Juan

Avalanche

kerry hanes · May 29, 2015 · Southern San Juan

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Weather

0430 at 10,660 in basin, 2/8's alto-cumulus, -2 C, calm. 0820 at 11,800 on SSE aspect below Twin Lakes, 4/8's alto-cumulus, +2 C, calm. 0930 at 13,000 on W aspect approaching Windom's west ridge, 4/8's alto-cumulus, -1 C, T-surf -2C, T-20 -1C. 1000 at 13,100 on N aspect of Windom's west ridge, 4/8's alto-cu and cumulus, -1 C, T-surf -2C, T-20 -2C, light W wind. See snowpack data for more. 1500 at 10,660 in basin 2-4/8's cumulus, +12 C. +12 C persisted until 1830. (Same period 24-hrs earlier saw a high of +4.5 C.)

Snowpack

At 13S 270549 4167067, 13,100', 1000-hrs, north aspect of Windom's west ridge, found a 30-cm deep layer of 1-mm facets with repeated Q1 shears with shovel shear tests and CT. CT scores were in mid-20's. A deeper (64-cm below surface) 4-cm thick layer of graupel, and a shallower (5-cm below surface) layer of graupel were also present, but had stronger interfaces than suspect layer. Decided not to perform further tests or continue approach to Windom. Skied a more stable slope west of test area on a north aspect--nice powder from 13,400' down to about 12,800', where a turn onto westerly aspects quickly became spring snowpack. The north slopes in this area (above 12,500', N aspects) were still in winter conditions with strong over weak layers of facets, rounding facets, significant graupel layers, and remarkably little sign of melt-freeze crusts. HS was over 3-meter deep in test location (probe did not reach ground). Below 12,500' on all aspects, we found spring conditions--hard supportable crusts until about 1000 and sloppy soft later than 1000, even on lower north aspects above treeline. By noon, most slopes below 11,500 were unsupportive.

Avalanche

See avalanche report on 5/26. In the same general area, significant spring shed occurred below 13,000, visible on NNW aspects in the Aztec-Kennedy area. From about 1530-1830, we saw a wet loose and occasional small wet slab avalanche occur naturally about every 10-min. Most originated in hanging snow fields above the major cliff bands and did not result in secondary slides when they landed on the lower angled slopes below the cliff bands.