Flagstaff, Arizona - Backcountry of The San Francisco Peaks and Kachina Peaks Wilderness
Format and Limitations Statement
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Winter conditions have returned to the Peaks with new snowfall, cold temperatures, and significant wind transport.
With new snow the ability to access backcountry skiing/snowboarding has improved. However, getting to and from good coverage may involve hiking over rocks and logs.
Avalanches may be possible near and above treeline where wind slabs have developed with continued wind transport from the south (S) and southwest (SW). Observations from the past week in Inner Basin Bowl and on Fremont Peak indicated continued wind slab deposits in Northerly aspects, increasing load on existing weak layers.
In addition to further wind slab creation, the presence of basal faceting has been observed on generally N facing aspects from ground level up to 30 cm (See attached snow pit diagrams), and has demonstrated failure and propagation on these facets, though spatially variable.
Cold temperatures and a relatively shallow snow pack may continue to build weak facet layers at ground level, below wind slabs and new storm snow accumulation. All of these factors could lead to heightened avalanche activity, especially on Northerly aspects and starting zones with recent wind loading and a bed surface.
Currently, year to date snowfall is at 55" (137 cm) at 10,800', with a settled base depth of about 33" (82 cm) on a sheltered NW aspect. 9,500' base depth is @ 17" (43 cm).
Above treeline snow has loaded leeward North facing slopes near ridge lines creating wind slabs that have demonstrated varying levels of stability. On Saturday and Sunday earlier this week, prior to the new storm systems, consistent SW winds were observed depositing smaller grains and forming harder wind slabs on weaker lower layers throughout the Inner Basin area on N- NW and NE aspects.
With similar conditions continuing, a greater likelihood of human triggered wind slabs exists.
With ~33" (83 cm) undisturbed settled snow depth at 10,800', NW aspect, coverage is improving but insufficient to cover many obstacles. Rocks and logs remain primary hazards. Most northerly aspects will have the best coverage with measured depths above 10,000 ft ranging from 20" - 48" (50 cm to 120 cm), while south facing slopes range from limited coverage to 28" (70 cm) in favored locations near treeline. Variable melt freeze crusts exist in the south facing snowpack.
Watch out for small isolated slabs of new snow, wind deposits and storm accumulation perched on older layers.
Watch out for wind slabs and/or wind loading on northwesterly, northerly, northeasterly and easterly slopes.
With a forecast of increased snow accumulation accompanied by moderate to strong winds wind slab creation will pose the greatest concern to back country travelers.
Although observations have found spatially specific wind slab locations, be cautious of more widespread wind deposition with wind directions forecasted to change and then return to SW predominance by Monday.
With accumulation of new snow onto existing bed surfaces, areas of instability may be present on all aspects. Be cautious of previously loaded terrain with slope angles exceeding 30 degrees, and runout zones which may hold more snow than starting zones.
Also, note that many south facing and wind scoured slopes may not have had coverage previous to this current storm cycle, thus use caution.