Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

It’s going to be a messy day—new snow, wind, warming temps, and rain all in play. Keep it simple and stick to sheltered terrain without big slopes overhead, especially if you make it to upper elevation terrain.

 

Problemi valanghivi

  • Storm Slabs

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

    Heavy snowfall at upper elevations will rapidly increase the risk of triggering a slab avalanche. Mid-elevation terrain will see a change from snowfall to rain at some point in the morning, but could also have similar new snow instabilities before that happens. Strong winds mean you are more likely to trigger a slab on leeward slopes and features, but there is enough new snow falling with rising temperatures that you should look for instability regardless of aspect or exposure to wind.

    Denser snow over weaker snow below is the first sign that a storm slab problem is building. Small slope cuts and hand shears can help assess bonding, but stormy weather, poor visibility, and reactive slabs favor conservative terrain choices. Stick to lower-angle slopes. Shooting cracks and recent avalanches are obvious signs to avoid steep terrain.

    (12/8/2023)

    Hand pits are a great way to look at the recent storm snow. Look for strong over weak layers and places it fails easily. 

    Photo: Andy Harrington

  • Loose Wet

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

    The size of any wet avalanches you see will depend on how much snow accumulates before snowfall switches to rain. If there is only an inch or two, you might not see anything more than a few rollerballs. But if snow stacks up deeper before rainfall, wet avalanches could become large enough to be dangerous. Avoid travel on or directly under steep slopes where you see fresh rollerballs or where the snow is turning mushy and wet.

    Rollerballs initiating from trees and other steep, rocky areas. These are indicators that more wet avalanche activity could follow. 

Avalanche Discussion

There are a couple of contributing factors that could make new snow accumulations on Tuesday more reactive than normal. The main one is that the new snow will fall on a sharp warming trend, so wet snow falling at warmer temperatures will build a slab over drier, weaker snow below. Also, a trace to a few inches of new snow that fell over the last few days has faceted and weakened and could make for a poor bond at the old-new snow interface. Faceted snow is probably more of an issue farther north in West Central or at upper elevations near North Cascades National Park. Finally, all this is accumulating over a firm crust.

One of these factors is reason enough to be a bit more on guard with fresh snowfall; all three of them together mean it’s quite likely new snow slabs will be more reactive than usual. This will primarily be an issue at and above 6000 feet, but you might also find dry, unstable slabs below that elevation in the morning.

NWAC Forecasters along the west slope of the Cascades found similar conditions on Monday, namely Low danger and thick crusts. But there were still some differences. Temperatures were warmer to the south–a high of 49F at the White Chuck Tripod at 5000 feet in West Central–so snow surfaces actually softened up even on shaded slopes. On the other hand, the mercury only topped out at 38F at the same elevation in West North, and the snow surface generally stayed firm, bumpy, and unforgiving. Stevens Pass may have been the sweet spot with corn-like soft snow conditions found on southeast through southwest aspects. The other big difference is the amount of new snow over the crust: little or none in West Central and Stevens Pass, compared to 2-4 inches farther north.

Regioni coperte