Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Wet loose snow avalanches will become possible today as last night's snow surface refreeze melts away. Avalanche danger will start out LOW early this morning while the snow surface remains frozen, increasing to MODERATE danger as the frozen surface melts away and deep wet snow develops. Please note that this is the last avalanche forecast for the 2020-2021 season.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Air temperatures were near to below freezing last night under clear skies across the forecast area. A decent to strong overnight snow surface refreeze is expected to have occurred. This will have been driven by either the below freezing air temperatures or by radiational cooling in locations where air temperatures were above freezing. Keep in mind that only the very upper snowpack refreezes this time of year and that there is wet snow below the surface crust that did not refreeze last night.

    Once the surface crust is nearly or completely melted away, the wet snow on the surface will combine with the deeper residual wet snow below it. This will create potentially unstable conditions and allow for the possibility of wet loose snow avalanches. Signs of wet snow instability include pinwheels, rollerballs, and sluffs of wet loose snow. Once these signs of instability start to appear or the surface crust starts to lose supportability, minimize risk by focusing travel on lower angle sub 30 to 35 degree slopes without steeper slopes above.

    In places where snow that accumulated earlier this week remains transitional with a surface crust over drier winter-like snow, larger wet loose avalanches remain possible on long steep slopes. Account for how terrain traps such as gullies, creekbeds, cliffs, etc. can magnify the consequences of an otherwise small avalanche.

Avalanche Discussion

* Variable amounts of storm snow from this past week were deposited on top of older melt-freeze snow across the region. In areas that received the least amount of storm snow, the recent new snow has either melted or assimilated into the existing melt-freeze snowpack. In some lingering areas where more than a couple of inches of storm snow accumulated, the upper snowpack remains transitional with a surface crust over drier winter-like snow.

* Variable roughness, firm snow surfaces exist in the morning. Most areas become soft and wet in the afternoon.

Régions couvertes