|Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
|Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
|Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.
|Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
|Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
|Likelihood of Avalanches
|Natural and human-triggered avalanches unlikely.
|Natural avalanches unlikely; human-triggered avalanches possible.
|Natural avalanches possible; human-triggered avalanches likely.
|Natural avalanches likely; human-triggered avalanches very likely.
|Natural and human-triggered avalanches certain.
|Avalanche Size and Distribution
|Small avalanches in isolated areas or extreme terrain.
|Small avalanches in specific areas; or large avalanches in isolated areas.
|Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.
|Large avalanches in many areas; or very large avalanches in specific areas.
|Very large avalanches in many areas.
On Friday we observed a couple large Natural avalanches from mid to end of the storm on 2.23. We also observed several small to large natural loose dry avalanches (sluffs).
We believe that numerous other avalanches occurred on 2.23 but they were challenging to identify due to the new 23-25% density snow.
Conditions have changed over the past few days. Photos below show smooth wind slabs and the effect winds have had on snow surfaces this week.
|Size (D scale)
|Unlikely to bury a person
|Can bury a person
|Can destroy a house
|4 & 5
|Can destroy part or all of a village
It will be possible to human trigger Persistent Slabs, 4 to 12″ thick, on all aspects, at all elevations, on slopes steeper than 35º. Natural avalanches are unlikely.
The February 22-24th storm brought less snow than anticipated, however, we did receive a shocking 2″ SWE (water) with 8″ new snow @IM 3550′ and 1.7″ SWE with 7″ new snow @Frostbite 2700. It’s hard to believe we live in a continental snow climate because this storm resembled what regularly occurs in a maritime zone.
In addition to moist snow, winds gusted SSE 17-25 mph for 12 hours on 2/23. Fortunately, dense snow takes stronger wind to build wind slabs which limited the size of the wind slabs.
We have not mentioned persistent slab as a problem in the forecast since January 28th, almost a month, which might be a record. It’s important to distinguish a persistent slab problem from other avalanche problems. Persistent slabs tend to hang out and persist in the snowpack longer compared to storm slabs and wind slabs which are short lived problems.
It will be helpful to dig in the snowpack, do pole tests, and instability tests to determine most likely locations for triggering a slab. Most likely locations will be where persistent slabs are sitting on near surface facets (NSF) on smooth bed surfaces like buried wind slabs, rain and sun crusts, have a shallower snowpack and/or slopes that have previously avalanched this season. The NSF layer formed during the cold weather Feb 19-21.
This video below shows an ECT with propagation failing on NSF and graupel on Friday on the south ridge of Marmot. We also experienced whumping/collapses in the snowpack on this layer prior to turning around.
The profile below shows the structure of this weeks new dense snow. On Friday we got propagation approximately 12″ deep that failed on NSF and graupel. We expect the buried NSF to be widespread, however, locations where the facets are sitting on old, smooth, crusts are more concerning and will be more likely locations to trigger an avalanche.
Pole/probe tests and formal stability tests will help you identify this problem. Whumping and shooting cracks will be red flags for this avalanche problem.
If you head into avalanche terrain today, utilize strict safety travel protocols, travel one at a time from safe zone to safe zone, only have one person on slope at a time, ensure all members of your party are carrying and know how to use beacons, shovels and probes, and avoid slopes with terrain traps.
2.22-2.24 Hatcher Pass received approximately 1.9″ SWE with 8′ new snow @IM and 1.7″ SWE with 7″ new snow @Frostbite. Winds gusted SSE 17-23 for 12 hours on 2/23.
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.