Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

A storm Sunday night and Monday will increase avalanche danger to Considerable. The day may start with avalanches mainly occurring on wind-loaded slopes, but wind deposits will probably be difficult to find and additional snow during the day will likely spread the avalanche problem to storm snow on all steep slopes. Shift your travels to lower angle terrain during your outing on Monday. 

Problemi valanghivi

  • Storm Slabs

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

    A few factors are going into the avalanche problem on Monday, but let's keep it simple: A storm will deposit around a foot of snow between Sunday night and Monday, and human-triggered avalanches are likely. Stick to slopes less than 35 degrees to avoid triggering avalanches and give the snowpack time to adjust. 

    Around 6 inches of snow could fall with strong winds overnight, so especially first thing wind drifted areas may be the location where you'll find large enough snow deposits and more reactive layers to trigger an avalanche. Wind will decrease into the light to moderate range during the day, and these wind slabs could be disguised under a less conspicuous, smooth layer of snow. As the snow builds, you can expect to find avalanches on non wind-affected steep slopes.

    Freezing levels will drop to 3000ft overnight, and then down to 1000ft into Monday. For the first time in a while we can expect to see snow at slightly lower elevation bands, and the Considerable avalanche danger may drop below treeline. Expect to find storm slabs at lower elevations, and as you work your way above treeline more slopes will have a wind influence, with drifted areas likely forming into larger and more reactive slabs, but don't discount non wind-affected slopes with deposits greater than 6 inches. 

    Snow forecast amounts vary, so be sure to evaluate areas where you're traveling to determine the extent of slab developments, and adjust the avalanche forecast based on your findings. Storm snow deposits will be shallow enough that you can use hand pits and test slopes to check the bond with the old snow layer. When in doubt, stick to slopes less than 35 degrees. 

    Storm slab avalanches like what you may trigger on Monday. 

Avalanche Discussion

In addition to new storm snow instabilities, we still have our minds on the infrequent large avalanches which occurred on wind-loaded near and above treeline slopes. Many happened Wednesday, 2/8, but an avalanche was reported late in the day Saturday in Canyon Creek, remotely triggered by a snowmobile. The large avalanche occurred on a 5400' north-facing slope, and was 2 feet deep. This was definitely something you wouldn't want to take a ride in. Most of the human-triggered large avalanches which have happened since the storm that ended on 2/7 have occurred in Canyon Creek, a location where you may be more likely to find this layer. The suspect layer is some mildy weak snow forms just above a crust. These are not typical wind slabs although so far the common terrain characteristics for these avalanches are near and above treeline in wind-loaded terrain. It is very difficult to determine whether a slope has this weak layer, so even if you dig you may not find obvious clues as to whether the layer of concern is present on the slope. 

Saturday was warm and moist, with a wintery mix falling to at least 5000ft. A few small natural avalanches occurred overnight, likely with a cornice trigger. All the surface hoar which was found the previous day was probably destroyed near the start of the incoming storm during the day Sunday. 

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