Haines Avalanche Center

Forecast Expired - 01/03/2021

Above 2,500ftModerate

1,500 to 2,500ftModerate

Below 1,500ftLow

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Wind Slab:

With winds from the north and snow in the forecast, wind slab hazard on specific terrain features is the primary concern. Human triggered avalanches for this problem remain possible. While the danger is mostly moderate, pockets of considerable do exist and will increase in likelihood of triggering, especially over any recent or deep persistent weak layers. An increase in wind speed/change of direction could indicate elevated hazard and make human triggering more likely. Identify suspect leeward slopes and look for visible signs of wind loading.  Strong over weak layering at the surface and a punchy feel tells you you’re on a slab. Be vigilant to any changing conditions, avoid run out zones, only expose one person at a time to the slope and stay away from terrain traps. Wind slabs can range from soft to hard, and predictable to unpredictable due to slab stiffness and spatial variability.

 

(Surface hoar near-treeline in the Transitional Zone 12/31. Once buried by wind slab or new snow these feathery crystals will become a dangerous persistent weak layer that will require extremely careful assessment and overall immediate avoidance in avalanche terrain. Photo: Tim Thomas)

 

Likelihood:

  • Almost Certain
  • Very Likely
  • Likely
  • Possible
  • Unlikely

Size:

  • Historic
  • Very Large
  • Large
  • Small

Trend

  • Increasing
  • Steady
  • Decreasing

Problem 2

Deep Slab:

Persistent weak layer concerns since early December are now buried under the weight of the new snow, and are deep enough that the likelihood of triggering one of these deep slab avalanches is unlikely. Remember that shallow, or thin areas in the snowpack could be ripe for access to these deep instabilities, especially above treeline where the snowpack is generally thinner than mid-elevations. Travel where the snowpack is fat and make assessments where it is not. This will help save some time digging. Think about how upper layers over the terrain could communicate to layers further down in the snowpack. Minimize exposure, use terrain wisely, avoid excess time in run-out zones, practice safe travel technique and remember how your decisions effect yourself and others.

 

(Deep slab avalanche trigger by a cornice fall. Notice how the slab stepped down to deeper layers and communicated between two shallow rock terrain features. Remember to imagine how the three-dimensional snowpack covers the underlying terrain. Photo: Tim Thomas)

Likelihood:

  • Almost Certain
  • Very Likely
  • Likely
  • Possible
  • Unlikely

Size:

  • Historic
  • Very Large
  • Large
  • Small

Trend

  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

Bottom Line:  Wind slabs will be an increasing hazard with the north wind and snow in the forecast. Widespread surface hoar and near-surface facets currently at the snowpack’s surface began to grow after the 12/29 storm cleared out, and two cold clear nights that followed. Moisture and fog from that event helped create a thin 1cm crust. This pencil hard crust with surface hoar over top sits above 3-5″ of softer deposits from Tuesday. Any current or future loading, either wind deposits or snowfall, that buries the surface hoar and weak snow at the surface will create a persistent weak layer.

Good News:  Before the new snow starts to fall, it is a great time to continue mapping the spatial distribution of surface hoar and make an observation to the HAC page. For the big picture, identify areas of shallow snowpack or underlying terrain. These could be rocks, cliffs, trees, vegetation, or un-supported slopes where it would be easiest to trigger deeper buried weak layers. Use informal slopes tests, such as getting off the track, digging quick pits, probing for strong over weak layering, and using low-consequence test slopes to help identify the avalanche problem and where avoid it.

*Keep in your decision making framework, the drawn out global pandemic response and taxed EMS resources*

Weather

Between 3-5″ of snow fell throughout the forecast zones earlier this week, as temperatures increased Tuesday before dropping quickly Wednesday. Latent moisture from the 12/29 storm produced areas of patchy fog closer to sea-level, while further up valley the night sky stayed clear, with cold overnight temperatures that promoted surface hoar growth at the surface. Increasing clouds, wind and snowfall is expected for the region through this weekend.

 Snow Depth [in] Last 24-hr Snow/SWE [in] Last 3-days Snow/SWE [in]  Today’s Freezing Level [ft]  Today’s Winds Next 24-hr Snow/SWE
Mount Ripinsky @ treeline   110″  0″ / 0.00  0″ / 0.00  0′  Moderate, N  2″ / 0.20*
Flower Mountain @ treeline  65″  0″ / 0.00  0″ / 0.00 0′ Moderate, NW   1″ / 0.10*
Chilkat Pass @ 3,100ft  38″   0″ / 0.00 0″ / 0.50 0′ Moderate, NW  1″ / 0.01*

( *star means meteorological estimate )

Additional Information

Practice like you play. Dust off your gear and make sure it is fully functional. Put new batteries in your beacons! Make sure everyone in the group has a functioning beacon, shovel and probe – and knows how to use them, keep your skills fresh. If you head into the hills, watch out for avalanche conditions, and be especially careful of rocks and hidden hazards like crevasses beneath the snow. WEAR A HELMET!

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