Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

New snow and moderate to strong ridgetop winds should create a fresh windslab problem at upper elevations. Expect a stormy day, with more new snow closer to the crest. Look for signs of instability like shooting cracks, and give large exposed slopes some buffer room as the storm passes through.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    New snow and moderate to strong ridgetop winds are likely to create a fresh windslab problem. Look for these at mid and upper elevations. The more exposed a slope is, the more likely you could find wind drifted snow. Check for signs of instability like shooting cracks. Look for clues to wind drifted snow like rippled surface textures, or observation of wind transport. Cornices are also a clue that past winds have blown, and Monday's westerlies are likely to drift snow onto those same slopes.

    Steer around large, steep slopes, especially if they get loaded from westerly winds. Use well supported terrain and consider not going underneath bigger complex features that could be actively loading from above while the storm rolls through.

     

    (1/5/2023)

    Example human triggered wind slab from about a month ago.

Avalanche Discussion

An incoming cold front should give Washington Pass somewhere in the ballpark of 5-9" by the end of the day on Monday. Areas further east are likely to pick up less snow, but ridgetop winds will be stronger. Over the weekend, observers have reported unreactive snow on steep terrain over the past couple of days, but snow surfaces became wetted with the warm temperatures on Sunday. Surface hoar was widespread on Saturday, but likely melted down in most places on Sunday. On Friday, observers near Harts Pass reported a recent cornice fall that triggered an 18" deep, and wide avalanche on an east facing slope. This slide ran on a thin crust, and stepped down another few inches to faceted grains. The rest of the snowpack was facets to the ground. This is an unusual snowpack structure for the zone, but it's worth keeping on your mind if you plan to venture to this area, or perhaps the far eastern edge of the zone as well. There are a few layers that we've been tracking in the upper snowpack. Aside from the February 3rd interface, the Jan 5th surface hoar (about 2-3ft below the surface) had previously been widespread and problematic in snowpack tests. With time and rounding of the grains, these layers are gaining strength. Older weak layers are more likely to be problematic during or shortly after any loading event, and to the far north or far east in the range. 

Almost 2 feet of snow accumulated from February 3-8th. Observers reported a number of large (up to size D3) avalanches throughout the Highway 20, Washington Pass area during this time. Crowns were mostly in north to east facing terrain, below cliff bands or in other wind-loaded terrain .Observers were able to trigger avalanches on the February 3rd interface just after the storm. A human triggered slide near the Lyall Glacier stepped down to a recent interface and broke into a large avalanche on an east aspect at 6,400ft. 

Regions covered