Numerous small natural wind slabs occurred mid-storm on Feb 14th when ESE winds gusted 20-31mph for 12 hours. These wind slabs failed just below ridgelines on SW to N aspects at upper elevation. One outlier was a larger slab avalanche on the NNW aspect on the Punk Spines at 3700′ in a zone we believe avalanched earlier in the season. For more info and pics of these avalanches see Thursdays forecast HERE.
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Loose dry avalanches (sluffs) will be likely to human trigger at all elevations, on all aspects, in protected terrain steeper than 40º.
With an additional 3 to 4″ of new snow in the past 24 hours, combined with 12″ of new snow from 2/11-2/13 the likelihood for triggering a sluff continues to carry the potential to injure or bury a person especially if compounded by the risk of a terrain trap. An additional 3 to 4″ of new snow expected over the next 24 hours will add to this avalanche problem.
Look for and pay attention to buried crusts up to 2 ft deep that will act as a smooth bed surface for sluffs to gain momentum. We have more recently found buried crusts in shallow isolated locations on southerly aspects.
Earlier in the week, we observed and received reports of people triggering and getting caught in small to large sluffs in steep terrain.
Getting caught in a loose dry avalanche in steep terrain may sweep you into terrain traps compounding the overall hazard. We mention this often because a significant amount of the terrain at Hatcher Pass involves navigating in, around, or above terrain traps.
We recommend avoiding terrain traps, skiing/riding one at a time, using appropriate safe zones, and using appropriate sluff management techniques.
Lastly, just because Loose Dry is the main concern of the day doesnt mean it is impossible to trigger a slab avalanche. As seen with the near miss on Wednesday, we can dig pits and gather data yet still miss a few pieces to the puzzle. Terrain features can make it challenging to recognize cross-loaded features and slopes that previously avalanched during the season will have a different structure. Few people have found evidence of buried persistent grains in the past few weeks, although it does exist in isolated and extreme terrain. We always encourage investigation of the snowpack, no matter the danger.
The winds had a mild and brief presence yesterday gusting SSE 15-19mph for 6 hours at 4500′. During our tour we observed 1-2″ thick wind slabs forming at 4000′ around 1pm. Expect these wind slabs to be 2″ thick, on W to N aspects, at upper elevation, and located at or just below ridgeline. These soft wind slabs will be easily manageable but also will become buried by an additional 3-4″ of new snow expected by end of day today.
On 2/17 winds from the SE gusted 16-19 mph for 6 hours at 4500′.
IM at 3550′ reported 3-4″ of new snow in the last 24 hours.
Frostbite at 2700′ reported 3″ of new snow in the past 24 hours.
NWS AVG Forecast here.
NWS point forecast here.
Marmot Weather Station here.
Independence Mine Snotel here.
Frostbite Bottom Snotel here.
State Parks Snow Report and Motorized Access information here.
XC trail grooming report for Mat-Su, Anchorage, and Kenai here.