Weekend Avalanche Outlook

This is a regional backcountry avalanche forecast for the Western Chugach Mountains of Chugach State Park. It is provided pro bono by a local avalanche professional, is based on limited field data for a large area, and is meant to be used only as a general baseline for recreationists’ personal and specific assessment in the field. The Anchorage Avalanche Center and associates assume no responsibility or liability for the use of this information. Anyone using this information needs to be formally educated in regard to avalanches and backcountry travel. Please encourage statewide investment in high quality outdoor and environmental education via K-12 public schools, as this is the best way to ensure all Alaskans are “avy savvy.”

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Get outside and enjoy The Greatland! This is your weekend avalanche outlook for March 6-8, 2020.

The avalanche danger this weekend is expected to be moderate. Be sure to practice safe travel protocols and effective terrain management to minimize exposure to potentially dangerous avalanche terrain and reduce the consequences if an avalanche is triggered.

A bit of new snow and moderate (potentially strong at times in some areas) winds are forecast for the Western Chugach Mountains this weekend. Snow, wind, cloudy skies, and poor visibility will complicate backcountry travel. If you’re recreating in avalanche terrain, make sure you’re prepared and plan for such complications.

Generally, the persistent slab danger is much more serious in northern areas of the park (i.e. Eagle River to Knik) where a thinner and “trickier” snowpack exists.

Problem 1 – Wind Slab

Human triggered wind slabs up to D2 (large enough to bury, injure, or kill a person) in size are possible on leeward terrain (primarily west clockwise through north aspects) steeper than 35º above 2500′.

Widespread wind-affected snow, with reactive wind slabs in some areas, existed prior to this weekend from the moderate to strong northwesterly winds that impacted much of the Western Chugach Tuesday-Thursday.  There’s still loose snow available for further wind-loading, and a few more inches of fresh snow are possible this weekend.

Wind slabs are most likely on steep and convex or unsupported terrain features.

Be on the lookout for red flags of wind slab danger (recent avalanches, shooting cracks, active wind loading). Pay close attention to the appearance and texture of surface snow: this is a way to identify potentially dangerous, wind-loaded terrain. Wind-loaded snow may look pillowy, bulbous, relatively deep (“fat”), and have a buffed or etched texture. Dangerously wind-loaded snow may feel hollow and punchy, indicating a denser slab overlying looser and weaker snow.

Pole probing and quick hand pits are a great way to assess wind slab danger near the surface. Expert skiers and backcountry travelers may be able to use prudent ski cuts to assess and manage the wind slab problem. However, wind slabs have the potential to “step-down” and trigger larger and more dangerous persistent slabs.

Remember that terrain traps can make even a small avalanche deadly. Be mindful of the consequences if you were to fall or lose control due to triggering just a small slab. Beware of exposure where a fall or slip could cause trauma, as well as channeled terrain features that might cause even a small amount of debris to pile up deeply.

Problem 2 – Persistent Slab

Human triggered persistent slab avalanches up to D3 (large, deadly, and destructive) in size are possible above 2500′ on all aspects.

While persistent slab danger is generally on the decline, it remains a lower probability but potentially very high consequence problem. A human triggered persistent slab may be very difficult to escape, as a person may be able to get into the middle of the slab before it releases from above with hard slab characteristics. The hard slab nature of the debris also makes trauma more likely.

Persistent slabs are expected to only release from terrain steeper than 35º and generally be stubborn for a human to trigger, but in some areas of the park (i.e. northern areas that have a typically thinner and trickier snowpack: Eagle River to Knik) it may still be possible to remotely trigger a persistent slab given further stress from recent and ongoing wind-loading. Be mindful of lower angle terrain where a hard slab may be connected to a steeper slope capable of producing a dangerous persistent slab.

Multiple persistent weak layers exist in the Chugach State Park snowpack. In general; basal facets and depth hoar exist near the ground, a significant layer of extensively faceted snow that developed December-January is buried mid snowpack, and thinner layers of less extensively faceted February snow are buried closer to the surface. These weak layers are sandwiched between wind-packed hard slabs of varying thickness. The relatively hard wind-packed layers may be able to bridge the weight of a human trigger, but if a weak spot is found (likely where the wind-packed, hard slab layer is thinner and/or less supportable) a dangerous avalanche could result.

Backcountry travelers in the Eagle River area alpine this week continued to experience collapsing (“whumphing”). Snowpits and stability tests continued to evidence propagation propensity on the December-January facets.

There is no effective way to manage this perplexing avalanche problem other than simply avoiding terrain capable of producing a dangerous persistent slab avalanche, especially steep and open slopes that are convex or unsupported. Assessment of this problem in the specific area in which you’re traveling will require thorough snowpack investigation: digging a snowpit, analyzing the stratigraphy, and conducting stability tests like the ECT.  As always, be mindful of red flags (especially recent avalanches, collapsing or “whumphing,” shooting cracks, active loading, etc.) and be very diligent about safe travel protocols.

Problem 3 – Cornice Fall

Longstanding cornices over typically leeward slopes (primarily west clockwise through north aspects above 2500′) are large in many areas of Chugach State Park. They are expected to grow larger and become more prone to falling this weekend, considering the forecast wind and snow. Give corniced ridges a wide berth; cornices may break off further back than expected. Do not approach the edge of a snow-covered ridge, unless you’re sure it’s not corniced. A cornice fall itself is dangerous, especially if the human trigger falls onto exposed terrain. Cornice falls may also trigger slab avalanches as they “bomb” the slope they fall onto.

Danger Trend

Increasing.

Mountain Weather

Expect cloudy skies, light snow at times, moderate winds, and alpine temps in the upper teens to mid-twenties.

Best wishes for your weekend!

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Funding and resources for this forecast generously provided by the Post-Capitalists and Libertarian Socialists of Alaska who encourage you to #FeelTheBern, #DumpTrump, #RecallDunleavy, and tell Murkowski, Young, and Sullivan that this is their last term! Our democracy and planet are at stake, stand up and fight the power!