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 February 7-9, 2020.
The avalanche danger this weekend is expected to be considerable. Dangerous avalanche conditions exist, human triggered avalanches are likely, and natural avalanches are possible.
The wickedly cold and dry January 2020 extensively faceted the snowpack. Snow and wind has since formed widespread hard slabs on top of very faceted weak layers. More snow and wind forecast through the weekend will further stress this deeper hard slab-weak layer problem, as well as building fresh wind slabs nearer the surface. This weekend’s forecast wind and snow will also build cornices, causing them to become more sensitive and prone to failure.
Problem 1 – Wind Slab
Widespread, touchy, D2 (large enough to bury, injure, and/or kill a person) wind slabs are very likely to be human triggered (and may be naturally triggered) on leeward terrain (especially west clockwise through north aspects) steeper than 35º at all elevations (but especially above 2500′). The previous surface snow in the Western Chugach has recently been buried by fresh snow and wind-loading. Previous, variable surface conditions are now widespread weak layers (heavily faceted snow) and interfaces (icy crusts and “boilerplate”) that may be overlain by very reactive (to stress from human and natural triggers) wind slabs from strong winds that picked up Thursday evening and may continue through the weekend.
Be on the lookout for red flags of wind slab danger (recent avalanches, shooting cracks, active wind loading). Paying close attention to the appearance and texture of surface snow 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 manage the wind slab problem. Wind slabs have the potential to “step-down” and trigger larger and more dangerous persistent slabs.
Problem 2 – Persistent Slab
Widespread persistent slab avalanches are possible on terrain steeper than 35º on all aspects and at all elevations (but especially above 2500′). The persistent slab problem is lower probability, but much higher consequence, than the wind slab problem. A persistent slab may be quite stubborn to trigger, but could fail catastrophically and produce a large and deadly avalanche up to D3 in size. The persistent slab problem is much less predictable, and a human triggered persistent slab is likely to be very difficult to escape. The trigger may be able to get into the middle of the slab before it releases from above with hard slab characteristics.
Heavily faceted snow (weak layer) sandwiched between dense, wind-packed snow (hard slab) has been found throughout the Western Chugach snowpack. Snowpits and stability tests are evidencing propagation propensity. Stout 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 deadly avalanche could result.
There is no effective way to manage this problem other than simply avoiding terrain capable of producing a persistent slab avalanche. Assessment of the 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 very diligent about safe travel protocols.
Problem 3 – Cornice Fall
Widespread pluming, wind-loading, and fresh cornice development beginning Thursday evening evidences the increasing cornice fall danger on leeward terrain (primarily west clockwise through north aspects above 2500′). Do not approach the edge of a snow-covered ridge, unless you’re sure it’s not corniced. Give corniced ridges a wide berth; cornices may break off further back than expected. A cornice fall itself is dangerous, especially if the human trigger falls onto exposed terrain. Cornice falls may also trigger wind and persistent slab avalanches as they “bomb” the slope they fall onto.
Mountain Weather
Unsettled, active weather is expected through the weekend: modest snow accumulations and strong winds. Temperatures will be relatively warm, and potentially above freezing into the alpine for a short period of time.
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 feel the Bern, dump Trump, recall Dunleavy, and tell Murkowski, Young, and Sullivan to GTFO!