Hatcher Pass

Three D1-D2 human triggered avalanches were reported by two parties on Saturday.

Marmot- near mid rib

Marmot-Catchers Mitt

Marmot-Lower convex rollover

A few natural slab avalanches were observed that likely occurred late night Friday. Obs here. 

12/23 Marmot mid-rib WSW 4500′

12/23 Marmot near the Catchers Mitt, W 3700′

Wind slab avalanches:  Strong winds persisted overnight, on average gusting ESE to E 33 to 48 mph over the past 30 hours stripping low density snow from windward aspects and building sensitive wind slabs on southwest to north aspects (clockwise) at mid and upper elevation.  It will be likely to human trigger a 6 to 12 inch thick wind slab on slopes 35º and steeper. Natural avalanches are possible.

Wind slabs that form on either firm bed surfaces or recently formed weak sugary snow (NSF near surface facets from recent cold weather) will be more reactive and have the potential to propagate further.

Common themes from the 2 parties who triggered 3 avalanches yesterday:

• Cracking in the recent wind affected snow was observed on the uptrack
• Whumping was not reported prior to avalanches
• Avalanches occurred above 3500′ on southwest and west aspects on slopes 35º and steeper
• Avalanches broke at skiers feet and were relatively small to medium in size, on average 6 to 10″ deep
• Both parties recognized the avalanche hazard as moderate and avalanches were possible in this specific terrain
• In 2 of 3 incidents skiers were caught, carried and not buried

Pay close attention to wind transported snow and avoid steep wind drifted terrain. Shooting cracks and sometimes audible collapses are indicators of instability. Look for hard snow sitting over weaker snow, smooth and rounded or lens shaped features. 4 to 5 inches of new snow today will make identifying wind slabs more challenging.

Strong ESE/E gusts have persisted over the past 30 hours and are expected to diminish this morning.

Persistent slab avalanches:

Consistent strong winds gusting E25-39 mph over the past 10 hours will keep persistent slabs on our radar as an additional avalanche problem today. There is a possibility that new wind slabs will fail deeper in the snowpack in the weak sugary snow sitting on firm surfaces.

It will be possible to human tigger a larger slab in isolated locations that fails 8 to 16 inches deep, on all aspects but most likely southwest to north aspects where wind slabs have the potential to overload weak layers deeper in the snowpack, at mid and upper elevation on terrain 30º and steeper. Finding these isolated locations may be challenging. Probe pole tests, hand shears, and instability tests will assist in finding these layers.

Travel protocols will be essential today. We will be choosing to travel one at a time and spacing out through avalanche terrain, paying close attention to utilizing safe zones well out of the way of the potential runout of avalanches, avoiding crowded slopes, and be digging test pits to improve the accuracy of our slope scale assessments and go-no-go decision making. Conservative choices will be key today, avoiding the largest and broadest slopes, and avoiding terrain traps.

Red flags:

• Our primary red flag to look for today is upside-down snow. This indicates a flaw in the snowpack that should be completely avoided. Simple probe testing or pole testing can easily reveal stiffer snow overlying weaker snow. Areas with a right-side-up snowpack exist, and if found harvest it.
• Curbing your desire with conservative decision-making will be key to your safety.
• Recent avalanches, shooting cracks and collapsing. These may not present themselves as a warning to an avalanche.
• It may take multiple riders to trigger an avalanche, and this may mislead you in your safety assessment.