Northern San Juan
AvalancheJeff Davis · Feb 2, 2019 · Northern San Juan
Weather
The morning started windy, cold, and clouds were moving in from the southwest. By the afternoon winds eased, temperatures rose, and and sunshine dominated the sky.
Snowpack
The snowpack above treeline ranged from 40cm's (on slopes that had avalanched) to 150cm's (on slopes that have not yet avalanche). On slopes with the deeper snowpack the middle of the pack is showing signs of strengthening. A 1 finger slab dominates the middle of the pack and ranges from 70-90 cm's thick. The caveat is this hard slab sits above 45-70 cm's of well-developed fist hard depth hoar and facets. Snowpack tests showed hard results on compression tests, but did not propagate. So what can we take away from this? Well many slopes in this area have been tested without incident, but those same slopes have previously avalanched, at least once. The trigger points area harder to find, but if you did trigger an avalanche it would likely be big. This is demonstrated by a large D3 avalanche that was recently triggered by an explosive nearby. Sunday, new snow is going to fall on a 5-10 cm layer of near-surface facets on dry slopes and a sun crust on sunny slopes. It is going to take a bit of a load for us to see avalanches step down to lower weak-layers, but avalanches in the new and wind-drifted snow will be easily triggered on steep slopes. Things have changed over the last week, but we are not out of the woods yet. The Persistent Slab avalanche structure persists on many slopes at upper elevation. Below treeline the snowpack continues to facet. Large surface hoar crystals were observed in protected areas. No cracking or collapsing observed today.
Avalanche
The mid-January avalanche cycle continues to impress. Many slopes in the Bear Creek and Alta lakes basin avalanches during this time period. Avalanches were observed with wide propagation and many ran full track.