Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
3 · Marcato
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

Avalanche conditions remain dangerous and you could trigger a large and destructive avalanche on steep south-facing, east-facing and north-facing slopes. Carefully planned travel, terrain management, and snowpack assessments are critical for safer travel in avalanche terrain today. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    What and where is it:

    You could trigger a large and destructive wind slab today on north, east, and south-facing terrain. Today’s problem encompasses older large wind slabs formed from February 4th’s snow, recently formed wind slabs from yesterday’s snow, and additional snowfall today that could continue to add to the size and sensitivity. 

    How can you recognize it: 

    If you have visibility, look for smooth, rounded pillows of wind-drifted snow as these will be the areas that you will be most likely to trigger an avalanche. Also, look for blowing snow at ridgelines for signs that new wind slabs are likely building and may be increasing the size of older slabs. If you are in softer, more reactive snow you may find shooting cracks under your feet or snow that is deeper than the top of your boots which are both signs of this avalanche problem. On firmer snow, you may notice a hollow, drum-like sound to indicate that you are traveling on a wind slab. The avalanches today have the potential to be large and if you find an older or firm slab it may give limited warning signs.

    How can you manage it:

    Terrain management will be an essential tool today. Limit your overhead hazard from both snow and other people, travel one at a time, and assess features that may be harboring a more sensitive wind slab like underneath ridgelines, cliffs, convex features, or in narrow gullies.

    A wind slab found on Summer Lion Head Traverse 2/6 

    Photo: Charlotte MacDonald

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    What and where is it:

    Old hard slabs are sitting on a buried persistent grain layer and continue to show the potential for instability above an ice crust bed surface. Forecasters have identified this structure as having the potential to slide on east and south aspects above 4000 feet. This faceted structure has been found in the snowpack, with specific areas like the Summit Snowfields and gully entrances on the south face of Tuckerman Ravine having sensitivity in snowpack instability tests. Additionally, on February 4th a very large avalanche on the Gulf on Slides Southern Snowfields stepped down to this layer and the possibility of this happening elsewhere remains. Note that one of the places this avalanche problem exists is just to the north of where the Lion Head Trail leads to Split Rock on the summit cone and on the Summer Lion Head Trail.

    How can you recognize it: 

    Identifying this avalanche problem is difficult without digging a deep pit, as there will be no visible clues. "Whumping" sounds as a warning are unlikely, and the slopes will likely appear unreactive.

    How can you manage it:

    Understanding where this problem exists in the terrain is the best way to minimize your exposure to the hazard. Plan your travel to avoid these isolated areas of a low-probability but high-consequence avalanche problem.

    Gulf of Slides Southern Snowfields 2/4 avalanche that stepped down to the persistent slabs below as you can see numerous crownlines

    Photo: Charlotte MacDonald

Avalanche Discussion

Overnight, the Mount Washington Observatory has observed hours of 50-65 mph west winds, but winds that were lower than the 70-90 mph and gusting to 120 mph which was initially forecast. These lower wind speeds have made travel in avalanche terrain today slightly more complex as there have not been hours of high winds that have hammered newly formed slabs into unreactive windboard. It is possible that in features exposed to wind that you will find very firm snow surfaces, but there is the potential for lingering stubborn sensitivity to persist. 

Wind-sheltered features and terrain management should be at the forefront of your mind and your travel plans today as you choose the terrain and hazards that you expose yourself to. The features to keep in mind that may have sheltered snow from wind will be areas underneath cliffs, below ridgelines, in narrow gullies, or steep convexities. You may find these areas to be incredibly wind-affected and unreactive, while others may remain softer and slightly more reactive. A last takeaway for today’s surface problem is to treat all wind-drifted snow guilty until proven otherwise. 

Looking at our other problem, there is some uncertainty around the persistent slab. Our listed aspects are areas where we have found poor, faceting structure and reactivity in instability tests. The buried ice crust where facets have formed on top was from a widespread rain event in December, so you are likely to find this ice crust at all elevations and aspects. We have been looking for this problem elsewhere and have not yet found it to have reactivity in northern aspects, and based on the snowpack structure in areas that we have looked at, it seems unlikely (Obs 1, Obs 2). This is something we are continuing to evaluate and something that you should continue to be mindful of. The recent Gulf of Slides avalanche showed that it takes an enormous trigger to step down to these persistent layers. However, with the potential for thin spots to lurk in the snowpack that will not be discernible from the surface, there is still a low likelihood but high consequence event of this being triggered by you.

OBSERVATIONS: Please consider submitting an observation on our website or in the new Avy phone app of what you are seeing in your travels. Submitting an observation hones your skills, informs other users, and improves our forecasts.

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