Here is a quick observation summary of last week from the GTSR:
Weather:
After a significant warm up last weekend (4/22-4/24), we settled into diurnal melt-freeze cycles along the GTSR corridor. Overnight temperatures tended to drop into the low 20s and daytime highs reached into the upper low 40s at 6000'. This was all accompanied by generally light winds and a trace to 3" of new snow during the week. We also observed the increasing strength of spring sunshine having a large influence on snow surface conditions and kept a close eye on cloud cover this week.
Snowpack:
Last weekend's warm up resulted in water percolating through the upper ~40cm of the snowpack and moistening much of the mid-April accumulated cold snow. Surface melt-freeze crusts developed overnight each night and tended to remain supportable to skier travel until approximately noon each day. The timing and locations of surface melt-freeze crust breakdown were largely dependent on direct solar input. By ~2pm each day, the upper 10cm of the snowpack was moist.
Avalanches:
We observed a widespread cycle of small natural loose avalanches (many started dry and ended wet) last Sunday and Monday including at least one skier-triggered avalanche in the Haystack drainage from a weekend recreational party. This cycle was largely confined to steep terrain above 6000', with some debris piles terminating over 1500' below due mainly to the specific terrain along the GTSR. As temperatures continued to fluctuate and freeze diurnally, the surface snow locked up and the natural wet-loose cycle shut down through Thursday with no new avalanches observed today.
