Weekend Avalanche Outlook
Issued Friday, March 3, 2017 at 10:25pm:
*Heightened Avalanche Conditions*
Evaluate snow and terrain carefully; identify features of concern. Human triggered avalanches possible. Small avalanches may occur in specific areas; large avalanches in isolated areas.
Touchy D2 human triggered wind slabs are possible on steep (>35*) leeward (primarily S to W aspects) terrain above 3000′. Recent natural and human triggered wind slab avalanches up to D2.5 in size have been reported. Active wind loading and cross loading has been evident in recent days.
Recent avalanches and shooting cracks are glaring red flags of wind slab danger. Pay close attention to the snow as you travel; wind slabs will typically be in areas with deeper snow where denser, firmer snow overlies looser, weaker snow or a crust. Punchy or hollow feeling areas of snow, and catchment areas with deeper snow (especially along leeward ridges and near peaks) are suspect. Quick assessment via pole probing and handpits will help you track the wind slab problem. Be especially mindful of terrain traps and exposure, which could compound the consequences of a small wind slab avalanche.
Stubborn D3 persistent slabs are possible in isolated areas above 3000′ on steep (>35*) terrain. This is a low probability, but high consequence problem that may exist on multiple aspects. These hard slabs may release unpredictably, above and around a human trigger, making escape difficult. Two persistent weak layers are still exhibiting reactivity in snowpit tests: a layer of buried surface hoar generally about 1-2′ down and the widespread layer of advanced facets and depth hoar at the base of the snowpack.
A more thorough snowpack assessment involving formal snowpit tests and layer analysis will be required to understand this problem. “Sweet spots” for human triggering of a persistent slab may exist in the upper elevations and include unsupported terrain (rollovers or convexities), thinner areas of the snowpack where a hard slab and either of these weak layers exist, and areas of the snowpack with small and sparsely protuding rocks where faceted snow may more easily be impacted from the stress of a human.
As always, practice safe travel protocols. Having an escape (or worst case scenario) plan in place will be important.
North winds have been transporting a lot of snow recently; sensitive new cornices may have developed in some areas as a result. As always, don’t approach a snowy ridge line to look down slope unless you’re sure it’s not corniced. Cornice falls are inherently dangerous, and they can also trigger an avalanche as they “bomb” the slope they fall onto. Give corniced ridges a wide berth; they have the potential to break further back than may be expected.
Expect clear, sunny skies this weekend with alpine temperatures in the teens to low single digits and light to moderate northerly winds.
Many avalanche accidents that have happened in Anchorage’s backyard of Chugach State Park could have been prevented by basic avalanche awareness. If you don’t have this level of awareness, here are some online resources to help you start the learning process. There are also numerous options for getting a real avalanche education locally.
*click avalanche problem icons and hyperlinks for further info