Lawinenlagebericht

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Human-triggered avalanches are likely today. While natural slides are possible, you will most likely be the trigger. Avoid wind-loaded features like drifts, pillows, and steep starting zones, and retreat if signs of instability are observed. Conservative decision-making should be at the front of your mind, given significant uncertainty and buried hazards (e.g., rocks, trees) lurking just under the surface.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Winds will continue to build dangerous slabs, especially on leeward slopes, gullies, and cross-loaded terrain features. Expect reactive pockets and slopes that will avalanche under the weight of a traveler, with natural avalanches possible.

    Avoid wind-loaded starting zones on steep slopes and cross-loaded features. Watch for cracking and be aware of hollow-sounding snow; both are obvious signs of instability. 

    (3/17/2024)

    Expect wind slab avalanches to be sensitive on leeward aspects and terrain features.

    Photo: Tanner Porter

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    The season's weather has created a complex snowpack that contains two persistent weak-layer problems (1) near-surface facets and (2) basal facets, each with their own distribution, and, if overloaded with new snow, could facilitate large avalanches (See Forecast Discussion for a brief season recap and what created these weak layers). 

    Given that the near-surface facets are closer to the surface and more likely to be affected by a backcountry traveler's weight, they are a primary concern. This weak layer is most likely present in starting zones that were less impacted by high winds over the last few weeks. Thus, expect this problem to be more prevalent in sheltered starting zones, lower-elevation starting zones, and areas offset from ridgelines. 

    The basal facets have been capped by the Holiday Ice Layer for almost two months, and failure of this layer will likely require significant new snow burden, as the holiday crust will likely bridge low to moderate loads. This means that this issue is likely confined to starting zones that (1) have maintained significant snow from the November snow and (2) have received a significant amount of wind-loaded snow from this week's storm (i.e., likely >3 feet).

    Given the complexity of this issue, assessing its likelihood remains challenging across the mountain and incorporates a significant amount of uncertainty based on snow accumulation and weak layer distribution. Based on recent snowpit observations, we view triggering an avalanche on one of these layers as a low likelihood but high-consequence event. Thus, for the time being, the only way to manage this uncertainty is through thorough slope assessment and conservative decision-making, or avoidance of steep and complex slopes.

Avalanche Discussion

There is significant uncertainty about conditions across the Peaks at the moment.  As an example, KPAC regularly uses 3 stations to gauge snowfall across the mountain, including (1) the Arizona Snowbowl stake (10,800'), (2) the Snowslide SNOTEL (9,700'), and (3) a remote stake in Snowslide (11,200'). These measures generally provide estimates of total snowfall and snowfall consistency across the mountain and different elevations. Unfortunately, this storm has been accompanied by high winds that have transported a significant amount of snow, creating disparities in accumulation across these sites. For example, on Wednesday the Arizona Snowbowl reported a storm system total of 16", while the remote Snowslide station (11,200') had not had any accumulation and actually lost snow (~6") between the start of the storm and Wednesday (2/18) at noon, as strong winds stripped soft snow from the previous storm. This disparity highlights uncertainties on the Peaks and underscores the need for thorough, slope-specific evaluations and conservative decision-making. While some slopes may harbor significant new snow and wind slabs, others may have been entirely scoured, with much of the snow being transported into the Painted Desert.

This storm's snow is falling on a complex snowpack that includes several potential persistent weak layers, which you should be aware of if traveling into the backcountry. A brief season rewind: a significant storm impacted the peaks in late November, followed by a generally dry and warm December. This period produced basal facets, although warmer periods moderated facet development. This dry period was followed by two significant rain events over the Holidays, which have plagued the season with the dreadful Holiday Ice Layer (HIL).  Following the Holidays, we have had several smaller storms that have fallen on top of the HIL, but this snow was often redistributed, stripping windward upper-elevation aspects, leaving the ice crust exposed. In areas that have maintained this newer snow, subsequent dry conditions have allowed it to facet, creating near-surface facets. These events have created a complex snowpack that contains two persistent weak-layer problems (e.g., near-surface facets and basal facets), each with its own distribution, and, if overloaded with new snow, could facilitate large avalanches.

Snow pits on Tuesday yielded ECTP9 at 15 cm and ECTP10 at 30 cm below the surface. Both broke at density changes in the new snow, highlighting potential instabilities.

Please remember that many south-facing slopes and areas above treeline have been stripped and melted to the ground or rock over the last few weeks. This new snow will hide many of the rocks and obstacles just below the surface.  Ski and ride with care, and watch for small avalanches or unusual conditions that could carry a skier or rider over steep or rocky terrain. 

If you get out, please submit your observations or email us at [email protected]. 

 

Remote Snowslide snow stake showing a loss of snow depth from the beginning of the storm to noon on Wednesday.

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