Hatcher Pass

There was a very active avalanche cycle last weekend:

• A snowboarder remote triggered a large wet slab avalanche on the SE aspect of Skyscraper at 4300’ at about 11:45 am Saturday.  Debris from this slide came very close to the snowmachine trail to the west side of Hatcher Pass.
• A skier reported remote triggering a small wet slab avalanche on the S aspect of Hatch Peak on Sunday.
• Many large natural wet slab avalanches, most gouging down to ground, have been observed last weekend and early this week. The majority of these slides have been on or under S to W aspect rocky areas.
• Many small to large natural wet loose avalanches, many gouging down to ground have been observed last weekend and early this week.  The majority of these slides have been on or under S to W aspect rocky areas.  Some of these triggered large wet loose avalanches below.
• No new cornice triggered avalanches have been observed this week, but cornices are weakening as temperatures increase, and are always unpredictable despite the temperature.

Large cornices have formed above leeward aspects and have released naturally over the last two weeks, triggering large avalanches that have stepped down and failed to ground in places. These large cornices have proven sensitive to human and dog triggers and should be avoided. Give cornices a wide berth as they can break back much further than expected and will be possible to trigger larger avalanches below. We should avoid traveling below cornices. Low visibility can make judging the size and safe route around cornices difficult. Cornices are extremely unpredictable.

Human triggered wet slabs will be unlikely at all elevations today. Temperatures were much colder both overnight, and during the day yesterday, than the ridge top highs of up to 40 degrees last weekend. However, even at 10 am yesterday, with an ambient temperature of 27 degrees, observers noted snow plopping off of rocks warming in the sun and water trickling down rock slabs at 4500’. The forecasted high temperature at 3500’ was 29 degrees F, yet the temperature was 33 degrees F at 11 am. It won’t take much power from the sun to warm rocky areas, especially on SW to W aspects, increasing the potential for wet slab avalanches.

Stepping off your snow machine or out of your skis to see if you are sinking in past your shins is a good clue you should head to lower angle terrain or a different aspect to recreate. Wet slabs can be remotely triggered and tests can be unreliable.

Wet slabs are unlikely at the lower elevations where the snowpack structure is mostly weak, lacking a slab component. However, wet slabs at mid elevations or upper elevations may run into low elevations so beware of being in run-outs under steep E to W slopes.

Similar to the discussion for wet slabs, colder overnight temperatures and daytime highs will make human triggered and natural wet loose avalanches unlikely today.

This does not mean there is no danger. Small avalanches are possible in isolated areas or extreme terrain, particularly among or under rocks, SE to W aspects below 2500’, on slopes steeper than 40 degrees.

With significantly warmer temps earlier in the week, many wet loose avalanches have gouged deeply through the snowpack and some have been large enough to bury, injure, or kill a person. Wet loose avalanches have also triggered large wet slabs on SE to W aspects.

Pay attention to rollerballs gaining momentum, sinking in up to your shins in the snowpack, and watch for wet loose activity on other aspects and terrain. These are all great clues the wet avalanche hazard is rising and indicators that it’s time to move to shadier and less saturated slopes to travel on. We should avoid traveling over or in terrain traps, as they amplify the consequence of even a small slide.