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 13-15, 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.

Recent weather has been relatively quiet, making for the least dangerous avalanche conditions we’ve had in several weeks. That said, potentially large and very dangerous low probability but high consequence persistent slabs still exist in isolated areas. In general, expect the persistent slab danger to be higher in northern areas of Chugach State Park outside the Front Range (the Front Range borders are Ship and Indian Creeks).

Localized, strong northerly winds earlier in the week wind-loaded leeward terrain in exposed areas: primarily the uppermost elevations, western and southern outskirts of the Western Chugach (along Knik and Turnagain Arms), and terrain adjacent to large valleys that channel outflow winds (e.g. Ship Creek). In such areas, more recently formed and smaller persistent slab avalanches (wind slabs formed earlier in the week) exist. These old wind slabs are becoming more stubborn but were still reactive to human triggers as of Thursday.

Temperatures are expected to increase significantly this weekend, especially in the alpine.  Increasing temperatures combined with a lot of sunshine (i.e. solar radiation) will significantly increase wet avalanche danger for the first time this season.

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 avalanche. 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 1 – Persistent Slab

Human triggered persistent slab avalanches up to D3 (large, deadly, and destructive) in size are possible above 2500′ on terrain steeper than 35º across all aspects.

The persistent slab danger is twofold: 1) isolated and lowest probability but potentially large, destructive, deadly, and very high consequence hard slabs failing on the December-January facets or basal facets and depth hoar near the ground 2) smaller, but still potentially dangerous and deadly, old wind slabs formed earlier in the week from the localized strong northerly winds.

Persistent slabs may become “reactivated” and more likely to be human-triggered on solar aspects (primarily southeast clockwise to west aspects), later in the day from a loss in snowpack strength due to warming temperatures and solar radiation.

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.

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-March 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.

Snowpits and stability tests continued to evidence propagation propensity on the December-January facets and more recently buried February-March facets.

There is no effective way to manage the perplexing persistent slab avalanche problem that is resulting from the extensively faceted December-January facets combined with a relatively high volume snowpack in the Western Chugach, other than simply avoiding terrain capable of producing a large persistent slab. The most likely terrain to produce such an avalanche is a steep and open slope especially if it’s convex, unsupported, and/or has thinner areas where the persistent weak layer is closer to the surface and more likely to be impacted by a human trigger.

Assessment of the deeper persistent slab 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.

In regard to the old wind slab problem that exists closer to the surface: 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 way to assess wind slab danger nearer the surface. Expert skiers and backcountry travelers may be able to use prudent ski cuts to assess and manage the wind slab problem. However, smaller slabs have the potential to “step-down” and trigger larger and more dangerous slabs as they descend.

Problem 2 – Wet Avalanches

Wet avalanche danger may increase significantly throughout the day on steep solar aspects (primarily southeast clockwise to west aspects). Forecast warm alpine temperatures combined with intense solar radiation, which the snowpack will be subjected to this weekend for the first time this season, are expected to make natural and human-triggered loose wet avalanches likely.

Loose wet avalanches and point-releases are most likely on rocky, solar aspects. Warming rocks will readily shed snow onto the slopes below them. These loose wet avalanches have the potential to trigger more dangerous persistent slabs as they descend.

Warmth and solar radiation may also de-stabilize persistent slabs.

It’s now the time of year when route planning needs to take aspect relative to the sun into consideration. Make sure your route does not expose you to terrain that has been de-stabilized by warm temperatures and the sun later in the day. This includes being mindful of overhead hazard, even if you’re on relatively flat terrain.

South and west-facing avalanche terrain and paths in the Turnagain Arm area are prime examples of overhead hazards and terrain traps.  Potentially dangerous, sun-exposed avalanche terrain and paths exist in the vicinity of popular hiking trails and nordic ski routes: Penguin Ridge, Bird Ridge, Indian Creek (i.e. Arctic to Indian), and Falls Creek. Make sure you know how to identify and avoid potentially dangerous, sun-affected avalanche terrain!

Problem 3 – Cornice Fall

Longstanding cornices (especially over typically leeward slopes: primarily west clockwise through north aspects above 2500′) are large in many areas of Chugach State Park. Cornices may become more prone to failure and falling this weekend on solar aspects considering relatively warm temperatures and intense solar radiation. Beware of overhead cornice fall hazard, as well as naturally triggered avalanches that may result from cornice falls.

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 throughout the day on solar aspects (primarily southeast clockwise to west aspects) due to warming alpine temperatures and solar radiation.

Mountain Weather

Expect a gorgeous and very pleasant spring weekend with sunny skies, light winds, and alpine temperatures in the 20s.

Best wishes for your weekend!

Please let us know what you’re seeing by tagging us on Instagram @anchorage_avalanche_center, submitting an observation, sending an email to info@anchorageavalanchecenter.org, or via FaceBook message. All observations help us provide the public with a better forecast product – no matter how basic. We are more than willing to keep observations confidential, and only use the information to inform forecast products.

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!