We were out with the UAS Level II course this Friday and Sunday. A temperature inversion that developed on Thursday continued through Friday, bringing above freezing temperatures but little or no precipitation to elevations above 500 m while cold temperatures prevailed below. The snow up high was moist on top, turning to melt freeze, and dry below, while the valley bottom snow remained deep and light. The thaw triggered a slab on Cropley Chute D004. Late Friday, a storm arrived and it began to rain to at least 800 m, wetting the surface layers and eliminating the inversion.

We did rescue practice Friday, not snow studies. But we still noted that the rain brought change and stress to the snowpack. Over Friday night and Saturday it triggered a couple R2 D2 size slabs on the Upper Fish Creek paths D001 and a couple small R1 D1 slabs on the upper NE bowl of Mt Stewart D003. Activity was not as much as it might have been because the snowpack had begun warming slowly long before the rain began. On our descent, the snow was changing but showed no sign of slab development on slopes to 40°+.

By Sunday, the rain had quit and we found soft snow with a runneled 2 cm semifrozen breakable melt freeze crust on top, moist snow to about 50 cm below the surface, and dry snow below. The facets from our recent cold weather remain sugary and weak, but the recent loading on them has been minimal, and the slab has warmed and moistened to the point where it is not very reactive, scoring a #4 on our slab test. On a 40° slope, a 75 Kg tester got the Rutschblock to release after multiple hard jumps (#6) on the main facet layer at 59 cm and on a thin localized layer of stellar crystals at 83 cm.

We set up two string and creep column sites to track snowpack changes over time on a south and a north aspect.

Slope tests did not reveal any signs of instability to 50°. The snow was a deep and rotten, with a grabby surface crust, but fat skis and snowboards turned easily in it.

The snowpack appears to have gone through a minor avalanche cycle as the thaw began and is now much less sensitive until further loading or heavy rains.

To make the creep column, a probe is carefully plumbed vertical, driven into the snowpack to the bottom, withdrawn carefully, and the hole filled with fine clay. When dug out later, the departure of the granular clay column from vertical indicates snow creep.