Large storm slabs sitting on a very weak layer of surface hoar continue to be LIKELY to human trigger at ALL elevations on Thursday. Conservative terrain choices will be Critical to playing safe out there for the next few days.
A weak layer of surface hoar buried mid January is down 40-120 cm and may be found on sheltered slopes near treeline in northern parts of the region. Deeper layers from early December and November can still be found in the snowpack. These layers may become reactive with additional snow load or in shallow, rocky, or thin to thick snowpack areas.
40-60 cm of recent snow has formed reactive storm slabs sitting on a weak layer of surface hoar. These slabs may be especially reactive in wind affected terrain.
WEDNESDAY NIGHT: Partly cloudy / Moderate, west ridgetop wind / alpine low temperature -15 / Freezing level valley bottom.
THURSDAY: Cloudy / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.
FRIDAY: Mostly cloudy / Strong, northwest ridgetop wind / alpine high temperature -5 / Freezing level valley bottom.
SATURDAY: Cloudy with flurries; 0-3 cm. / Moderate, west ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.
On Tuesday, several skier triggered storm slabs up to size 2 and numerous explosive triggered storm slabs up to size 3 were reported near Golden.
Most notable was a report of skier remotely triggering a size 2.5 storm slab from a ridgetop at treeline near Quartz Creek. This avalanche failed on the very weak layer of surface below the recent storm snow. It was reported that light wind effect had stiffened the recent storm snow just enough to be highly reactive to skier triggering. Min report HERE.
Touchy storm slabs are sitting on a weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.
Overnight flurries deposited up to 15 cm of new snow in the central portion of the region near Panorama. Recent snow totals are now 40-60 cm. The bulk of the snow on Sunday/Monday fell with warm temperatures and moderate southerly winds, both of which increased slab development and reactivity within the new snow. This recent snow may be sitting on top of a layer of surface hoar which would greatly increase the reactivity of the newly formed slabs to human triggers, as well as the size of avalanches. However, the size and distribution of this layer is uncertain.
70-110 cm. down is an older surface hoar and/or a thin melt crust from mid January. This layer was more prominent in the north Purcells in sheltered, open slopes at treeline.
Two deeper layers persist, though they have been recently unreactive. Down 140-180 cm lies the December weak surface hoar / crust / facet layers. Closer to the ground lies the early November crust facet complex. Though unlikely to trigger, caution for these layers remains with large loads in steep, shallow, rocky areas with a thin to thick snowpack.
