Bollettino valanghe

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

Today, a skier or rider is likely to trigger a wind slab or persistent slab avalanche in steep terrain near and above treeline.   These avalanches may fracture 1' - 3' deep in the snowpack and could result in a full burial. The most probable locations for these problems include loaded ridgelines, convexities, and steep avalanche paths.  Backcountry travelers are encouraged to stick to low-angle terrain and avoid wind-loaded pillows, wind drifts, hollow-sounding snow, and cross-loaded gullies.

Problemi valanghivi

  • Wind Slabs

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

    Varying wind speeds, directions, and storm temperatures have created an upper snowpack with alternating densities, and thus wind slab remains the primary avalanche problem on the Peaks.  Since Friday morning, elevations near treeline and above have received over 2' of new snow, with 5-9" of that occurring last night.  Today, unsettled weather is expected to continue with 2-4" of additional snow forecast for 11,500' and winds gusting as high as 15 mph.  In a snapshot, there's plenty of snow available for transport, and the wind has had its way with it.  Primary winds in the last two days have impacted the peaks from multiple directions, and localized winds have been swirling erratically and loading slopes of all aspects. 

    Those entering the backcountry should be aware of the likelihood of wind slab avalanches on all aspects near and above the treeline.   These avalanches could step-down and trigger a larger avalanche on the persistent weak layers buried beneath the new snow.

    Wind slab avalanches throughout this storm cycle have fractured in broad and unexpected ways.  Widespread evidence of this problem was found on Saturday and Sunday, with most backcountry parties experiencing shooting cracks or fractures on test slopes.  Very few reports have materialized on observations at higher elevations and in the Inner Basin zone; if traveling in these areas, proceed slowly and be wary of top-down circumstances where wind slab avalanches may be released on the leeward side of high-elevation ridgelines. 

    Skiers and riders are advised to proceed cautiously and be on the lookout for cracking and shearing.  Be wary of the leeward side of slopes, and look for mounds of snow with textured surfaces at the top of gullies and near small terrain features.   Utilize small test slopes, such as a few feet above the skin track, to check for shooting cracks and determine how reactive wind slabs are to the weight of a skier or rider.  Avoid the temptation to keep pushing into higher, steeper terrain, as wind slabs may be lurking beneath soft, low-density surface snow. On Sunday, these slabs were preceded by widespread cracking, up to 10' in length.  If these signs of instability are observed, be prepared to retreat and stick to low angle or below treeline terrain.

    (3/17/2024)

    A small (D1) wind slab avalanche on a small test slope. 

    Photo: Tanner Porter

  • Persistent Slabs

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

    Facets in and below the mid-level of the snowpack may reach a critical threshold and result in a slab avalanche with the additional weight of a skier or rider.  Recent accumulation and transported snow have complicated this situation.  Current weak layers have been found ranging from radiation-formed facets above melt-freeze crusts, 1' beneath the surface, and as deep as 3' pre-storm.  It is possible for a wind slab avalanche to "step down" and trigger these persistent weak layers in isolated terrain, resulting in a larger avalanche.  

    Facet layers are notable for forming above solar crusts and have been observed in specific areas on west, north and south aspects. These solar crusts are facet factories when insulated deeper in the snowpack, and these newly formed weak layers will need to be monitored in the coming days.  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 avoid the runout zones of overhead avalanche paths. 

    (3/14/2024) Our current PWL to track which is 30-50cm beneath the surface. On northern aspects, midpack facets are set up above a solar crust. On southern aspects, facets are layered between multiple melt-freeze crusts.  Photo: Eric R./ JP

Avalanche Discussion

Over 2' of snow has been deposited on the San Francisco Peaks over the last 5 days.  Complicating the situation have been moderate winds that have affected localized areas from nearly all directions.  The varying wind speed, direction and storm temperatures have created a highly layered upper snowpack of alternating densities.  These conditions warrant caution and acute observation, as the reactivity of conditions can rapidly change.  

Avoidance is the name of the game at this stage.  Due to limited visibility and evolving weather patterns, observing natural avalanches in the full extent of our forecasting area has not been possible, therefore uncertainty still remains high for wind slab potential. 

The hazard is difficult to assess, as there have been limited observations on much of the mountain since Sunday.  Fresh wind slabs don’t necessarily need to be very stiff to carry or bury a human, as any snow that has drifted into a deeper slab will be suspect and harder to assess.  Be skeptical of slopes with relatively stiffer snow sitting on top of a softer layer. Warning signs like shooting cracks and collapsing, are clear indicators of unstable snow. Cracking is evidence to support your suspicions of instability, typically in the upper surface of the snowpack.

The most common, though not the only, areas to find reactive wind slabs today will be in moderate to steep terrain just below ridgelines, convex rolls, and gullies. Travel tests can be a very effective way to assess how sensitive these surface problems are. This includes things like quick hand pits to see how easily the new snow is shearing off the surface. 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.  Snowpack assessments, safe travel techniques on negotiable terrain and maintaining a high level of suspicion is a best practice going forward.

Collapsing, found on northeast to northwest aspects, as well as south-southwest aspects, may again be a theme of the day as the new-old interfaces are adjusting to the new weight of freshly transported snow.  With the additional snow from last night, it is uncertain how the buried weak layers will react.  Due to this uncertainty, maintain strict travel precautions and avoid exposing more than one individual to hazard at a time.  Create a plan with decision points, utilize safe traveling techniques, and avoid having a runout zone above you.

Many areas of our forecasting zone were previously stripped or shallow with rock, talus, and vegetation exposed on the surface. With the recent accumulation of soft snow, areas that have been sheltered from the wind or nearby may be harboring hazards that may deceive the unaware traveler. Maintain caution and feel beneath the surface often and at multiple aspects, to avoid an injury from being caught off guard or thrown off balance, in simple to challenging terrain.  

Storm totals so far are 35" reported from Arizona Snowbowl and 21" at the Snowslide Canyon SNOTEL.  3.7" of SWE has been recorded at the Snowslide Canyon  SNOTEL site since Thursday. 

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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