Forecaster Observation - Lost Johnny, Swan Range

We spent the day in the upper end of the Lost Johnny drainage.  Our objectives for the day were to assess instability due to warm temperatures and sun exposure, and look at potential water percolation through the snowpack.

The snowpack was frozen and very solid on the way up.  We didn't see much warming effect on the road/trail until close to 11:00.  After that temperatures were well above freezing and the snow softened up enough to cool the machines and provide good traction for skinning.

There is evidence of widespread wet loose avalanche activity up to size D2 (large enought to bury, injure, or kill a person).  All aspects showed debris in the runout zones, with several piles even making it to the Lost Johnny Road near the end of the road.  We observed two slab avalanches. One of these occurred while we were standing on the ridge nearby earlier in the morning.  It was on NE aspect, 6800 feet and was the result of a cornice fall onto a wind slab. We also noted large cornice formation along ridgelines in the area (photo).

We dug two pits, either side of the Swan crest at roughly 6950 feet.  On the NE aspect we had 150 cm of dense wind affected snow before finding a crust.  There were several density changes within this slab, and one layer of graupel.  We had no results in our Extended Column Test.  In a Compression Test, however, we did find a weak layer 20 cm down(CT14).  This was the interface between the saturated snow and the denser, drier snow.  Coincidentaly this was also where we found the graupel layer. 

On a south aspect the snowpack was shallow (118 cm) and moist throughout (photo). The upper 18 inches of the snowpack consisted of large, wet grains. 18 inches from the surface was a prominent crust that had water pooling above it. The only result in stability tests were on a decomposing crust 6 inches from the surface (ECTN15, CTM 14).

From a distance we could make out a small crown on a nearby peak above Lamoose Lake, we rode over to get a better look and found that a cornice had failed and triggered an avalanche in recent windslab. See Avalanche Observation.