Bollettino valanghe

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche danger remains MODERATE at and above treeline. Triggering an avalanche 2-3’ deep on a buried weak layer, complicated by recent wind loading, is the main concern. Wind slabs up to 1' are also possible. Where this problem exists is difficult to find in terrain, so a cautious and conservative approach are best practice if recreating today. Carefully evaluate surface conditions at mid and upper elevations, especially below loaded ridgelines, convexities, and steeper loaded gulleys.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The primary layers of concern for triggering an avalanche exist at the new snow/old snow interface 2-3' below the surface. Wind effect 72 hours ago and as recent as this morning, has further exacerbated our persistent slab problem by hardening surfaces with weak layers beneath. Current weak layers include radiation-formed facets above and below melt-freeze crusts and facets associated with the pre-St. Patrick's storm dry period.  Potential remains for an isolated wind slab or wet-loose release to "step down" or create an additional load on the underlying persistent weak layers.  Though continuity across larger, broader slopes remains isolated, one can still be thrown off balance, caught, injured, or buried in the right location at the right time. Depths near ridgelines are widely variable, from bare surfaces to generally 140-180 cm at loaded starting zones. 

    These persistent weak layers are difficult to assess and can give travelers misleading feedback during assessment. Some techniques used to assess new snow problems such as hand pits and test slopes are usually not reliable for these persistent slab problems.  Signs like shooting cracks or collapsing are clear indications of dangerous conditions, but we might not always see these even when conditions are optimal for triggering an avalanche. Instability tests may be able to tell you a little bit more regarding propagation propensity, but ultimately it can be difficult to distinguish the spatial distribution of a persistent weak layer throughout multiple aspects and terrain.

    On Wednesday,  a D2 avalanche was triggered on the skin track out of the Humphrey's Cirque (HS-ASr-R1D2-I).  This avalanche was remotely triggered by a collapse and shooting crack that ran towards a rock outcrop and could have gone larger.  Fortunately, no one was caught in this event.  This avalanche did propagate but did not release due to surface tension within the snowpack.  See the avalanche observation and additional photos here.  It was released on an old snow/new snow interface, specifically on facets above a thin, harder layer that was likely a solar or wind crust. 

    (3/20/2024)

    The D2 slab avalanche remotely triggered on the skin track exiting Humphrey's Cirque.  This avalanche was nearly larger as a substantial crack permeated an additional 100 feet beyond the crown but did not propagate.  Fortunately, no one was caught in this event. 

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    The potential for a skier or rider to trigger a wind slab avalanche remains unlikely today, but triggering a 1-2' slab is still possible in isolated terrain, especially in steep rollovers, near loaded gullies, and in starting zones due to increasing wind loading and cross-loading effects.  As winds increase into tonight and tomorrow,  keep an eye out for the increased likelihood for wind slabs to form in unsuspecting terrain. 

    It is possible that a human caused wind slab avalanche could trigger a larger avalanche on the persistent layer.  Loaded convexities, entrances to gulleys, and leeward slopes are key locations for slab development and hotspots for triggering an avalanche. To identify areas with wind slabs, keep a lookout for stiff or hollow-feeling snow in wind exposed areas and by pole probing for stiffer snow over softer snow. Utilize small and inconsequential test slopes to check for shooting cracks to determine how reactive wind slabs are to the weight of a skier or rider. Ensure you avoid the temptation to keep pushing into higher, steeper terrain, as wind slabs may be lurking beneath softer surface snow. 

    Despite the melt freeze crusts on the surface at low and mid elevations on southerly, westerly, and easterly aspects, it is still possible that increasing winds  will transport snow at upper elevations, potentially stiffening existing surfaces or loading windward slopes. 

    (3/20/2024) Photo: Blair Foust

    A view of the artificially triggered avalanche resulting from AZSB ski patrol control work on Wednesday morning.  (HS-AEc-D1.5-R3-S)

Avalanche Discussion

In general, we have seen more propagation in our pits and with human-triggered activity this week, compared to the previous weeks.  Even though facets are typically labeled as weak sugary snow at a specific depth, the currently widespread and variable facet layer is showing evidence of being notably thinner with variability in hardness which makes it difficult to replicate in adjacent terrain in instability tests. Our forecasting area is within the pattern of experiencing consistent overnight freezes and above freezing daytime temperatures. The trend towards spring has arrived a bit early, but pulses of unsettled weather are surrounding the San Fransisco Peaks once again, which calls for strong shifting winds and snow accumulation. The avalanche hazard will potentially increase over the next few days and the need to pay attention to subtle clues the snowpack, weather and specific terrain is trying to show is paramount to getting out and returning home safely. 

Yesterday, a party traveling below the B-24 site headed towards Allison Clay on a NNW aspect received small-column test results that indicated a reactive snowpack, on a persistent weak layer, (CT15 SP, 70 cm down on facets). This observation indicates both the increasingly reactive mid-pack persistent weak layer variability and just as important, the keen decision-making skills based on practical and representative assessments. The group decided not to ski the N aspects of Allison Clay, and instead skied down towards AZ Snowbowl via Dutchman's on less consequential and manageable terrain. An excellent (and much appreciated!)  video of the group's compression test (CT) can be found here. 

Facet layers are notable for forming above solar crusts and have been observed in specific areas on both northerly and southerly aspects. These solar crusts are facet factories when insulated deeper in the snowpack and typically time will either help bond snow to the crusts or create a larger, more developed weak layer. These problems are tricky to predict and even harder to assess. The best way to manage this type of avalanche problem is to take a more conservative approach to selecting terrain by sticking to lower angle slopes and avoiding the runout zones of overhead avalanche paths.

Many areas of our forecasting zone are still harboring shallow or completely stripped surfaces with rock, talus, and vegetation exposed on the surface. Take note of depths when crossing slopes and maintain a keen eye for chutes and ridgelines that may be only a few inches deep. Striking a rock, stump or dirt patch at high speeds can result in serious injury. Your best bet for staying out of trouble and finding the best surface conditions to ski or ride is to look for slopes that are protected from the wind today.  As weather conditions deteriorate, be vigilant in preparation for the backcountry and implement decision points along your ascent, during a snow pit, between transitions, and before every descent to ensure partners are on the same page. Risk management is effective when voices and mindsets are aligned.  As always, employ safe travel techniques on negotiable terrain and maintain a high index of suspicion on this tricky set of problems. 

Storm totals from the last cycle are 35" reported by the Arizona Snowbowl at 10,800' and 21" at the Snowslide Canyon SNOTEL with 3.7" of SWE.  Enjoy these last little bits of powder skiing before the spring corn cycle sets in. 

Come join Kachina Peaks Avalanche Center on Saturday, April 6th, at the Agassiz Lodge deck for the Mikee Linville Fundraiser!  All proceeds from this event go to our scholarship fund, which, to date, has resulted in over 29K of scholarship benefits!  For more information on how to get involved, visit kachinapeaks.org.  Many thanks to everyone who made our avalanche courses a success this season and a big thank you to all our participants!

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