Hatcher Pass

13″ New snow and moderate to strong winds were responsible for numerous avalanches this week.

For more info on the Natural and Human triggered avalanches from March 12 , check out the mid week summary, HERE or weekly OBSERVATIONS HERE.

Natural avalanches were also observed on March 14 and 15th, although exact details can not be confirmed due to poor weather conditions and low visibility. Most slab avalanches were observed on SW through NE aspects at mid and upper elevations and ranged from 6″-18″ deep, mostly small, but up to D2,  large enough to bury, injure, or kill a person.

Above: Wind slab avalanche below Marmot ridge, 4000′ W aspect, likely 3/14.

Above: Small wind slabs failed naturally on side walls of Marmot Mid-Rib, likely 3/14. Photo shows debris on the left, bed surface in the middle, cross loaded and sastrugi to the right. NW aspect, 3600′

3/14 D2 natural wind slab that appears to have stepped down. NW Martin Mine Gully 3900′. Picture HERE

Strong winds gusting E/SE 22-53 mph on 3/13-14 combined with gusts avg ESE 34 mph overnight will contribute to a wind slab problem today at mid and upper elevations, on slopes above 35º, on West to NE aspects, and cross-loaded SW aspects. Anticipate slabs to be shallower, 6-12” on cross loaded SW aspects, and 12-18” on leeward aspects, W to N.  It will be possible to human trigger hard wind slabs today, 6″-18″ deep, up to D2, potentially large enough to bury, injure, or kill a person. Small avalanches in specific areas or large avalanches in isolated areas. Natural avalanches are unlikely.

Wind slabs are often smooth and sound hollow. Use visual clues to identify wind loaded terrain features and avoid them. Wind slabs are mostly 1F to P hardness, and may allow your weight to get out on them before breaking. Cracking, whumping, or collapsing are signs of instability, and were observed on 3/15. The most likely places to trigger a wind slab today are steep gully side walls, near and below ridgelines, and on cross-loaded features. Strong winds have also deposited wind slabs mid-slope, well below ridgelines.

Below: Marmot winds from 3/13-14 that have contributed to building wind slabs this week.

More about wind slabs in the avalanche problem toolbox, HERE.

Wet-Loose: The lack of a solid freeze overnight at 3550′ and temps already 11ºF warmer than yesterday morning, will contribute to an increase in wet-loose  activity from LOW in the morning to MODERATE in the afternoon on steep Southerly,SE to SW aspects, at low and mid elevation.  South aspect structure HERE shows the stout 3-4″ thick melt freeze crust. This crust varies in thickness and strength with elevation and aspect. Watch this crust carefully.  Once the bonds weaken, there will be plenty of eager facets, persistently waiting under the crust to contribute to the avalanche problem, increasing the size and consequence of any wet-loose.

Persistent Slab: Although triggering a persistent slab will be unlikely today, small avalanches in isolated or extreme terrain will be possible. A few persistent slabs avalanches occurred this week in paths that previously failed this season (aka repeat offenders), for example: Martin Mine, Hatch, April Bowl, the the Willow side of HP. In general, these isolated locations have a shallower snowpack, more persistent grains, and failed from a new significant wind load.  It will likely take another loading event for these deeper persistent slabs to fail.

Cornices: Strong winds transporting new snow this week have contributed to building even larger cornices. Many cornices at upper elevation leeward aspects are overhung and may support you stepping on them before breaking.  Give yourself a wide berth when travelling in and around cornices. Cornice fall can injure or kill you and trigger other avalanche problems. Flat light will make cornice assessment challenging.