Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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

Avalanche danger is LOW for all elevations. Small loose wet avalanches may occur today. Deep slab avalanches are very unlikely but not impossible on a regional scale.

Problemi valanghivi

  • Loose Wet

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

    Air temperatures at 0600 this morning at the upper elevations are 6 to 8 degrees warmer than 24 hours ago and are above freezing. Clear skies and radiational cooling last night are expected to have allowed for some overnight snow surface refreeze despite above freezing air temperatures. The warmer sunny start to this morning, forecast daytime air temperatures above 7,000' well into the 40s, and the possibility of evening rain will combine to increase the likelihood of loose wet avalanche problems today into tonight. Avalanche size is expected to be small and could occur on any aspect.

    Look for fresh roller ball activity as a sign of instability. If in doubt avoid steep slopes where any signs of wet snow instability, either new or old are present.

  • Cornices

    • Tutte le quote
    Probabilità
    Possible
    Dimensione
    0

    Triggering a deep slab avalanche is very unlikely on a regional scale but cannot be ruled out entirely. Most snowpack data points to significant improvements in stability over the past week, but a few outliers exist. Keep in mind that in the unlikely event that a deep slab avalanche is triggered, avalanche size will be large (up to D3). Factor large avalanche size into travel plans and route selection on NW-N-NE-ENE aspects. If in doubt, increase the margin of safety by choosing less complex terrain and increasing the distance from areas of exposure to potential avalanches.

    The main focus of the lingering deep slab issue is not so much on an avalanche occurring today, but on monitoring of the layer of concern to determine how it may respond to new snow loading by the series of storms forecast for the remainder of this week.

Avalanche Discussion

* Sun and warming have continued to affect the snow surface in most areas, including many N aspects below about 8,500'.

* Observations made yesterday on Elephants Hump (Carson Pass area) on a previously fractured and investigated slope showed a significant stability increase of the faceted weak layer associated with the recent deep slab problem.

* Observations received yesterday from Powderhouse Peak (Luther Pass area) pointed to isolated, lingering instability of the deep slab problem.

* Other observations over the past week from around the forecast area targeting the recent deep slab problem have overall shown signs of increasing stability. Outliers continue to present, most recently from the Luther Pass and Echo Summit areas. General trends in snowpit data are that the once faceted weak layer of concern is located 3 to 6 feet deep in the snowpack on NW-N-NE-ENE aspects, remains significantly less dense than the slab above it, and often presents as loose grains. Varying degrees of rounding of the once faceted snow have be observed. In some locations, faceted crystals are no longer visible under magnification. In other locations, striated faceted crystals remain. Snowpit tests mostly indicate that it is difficult to trigger weak layer failure (ECT, CT). There are some exceptions. Tests specifically examining propagation potential (such as the PST) tend to indicate that propagation could still occur along the weak layer in the unlikely event that snowpack failure is triggered.

Regioni coperte