Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Unsurvivable avalanches up to 7ft deep remain possible in the zone, as do wind slabs and wet loose avalanches. Saturday is not the day to step out into big features, but a day to be very conservative and disciplined in your terrain choice. Avoid steep open slopes, and give the snowpack time to settle out after significant snowfall and avalanches this past week. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3

    The uncertainty and unpredictability of deep and persistent slab avalanches should determine where and how you travel. Avoid going into steep slopes, or underneath areas with large slopes above you. Avoid traveling on and beneath slopes 35 degrees and steeper. Slopes 5,000ft and higher and on east to south to southwest aspects are the most concern and have recently produced avalanches over 1,500ft wide and up to 6 feet deep. 

    A persistent weak layer involving facets on or within a crust that was buried in mid-January has plagued the snowpack with lingering instability for over a month and a half. While south aspects appear to have been especially problematic, we know persistent slabs have also run on shaded slopes. Unfortunately, this problem isn't going away for a little while, and we shouldn't be surprised to hear about more of these monsters in the coming days. Saturday is not the day to step out into big terrain, but a day to let the snow settle. 

    (2/24/2021) Very large avalanche reported from a South aspect at 5,500ft near Manastash Ridge on the 24th. This instability will continue to be a problem in the near future.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    You'll find lots of recently wind-loaded slopes to be careful around. Slabs may be stubborn to trigger, but if you do trigger one it could be large or even step down to become a very deep and destructive avalanche. Wind slabs may be resting over weak layers of buried surface hoar and could act in surprising ways. With this, and the potential for deep or persistent slab avalanches, you should avoid large steep slopes, especially at mid and upper elevations. Avoid wind-loaded, leeward slopes 35 degrees and steeper.  Below treeline, stick to wind-sheltered slopes and well-supported features. Watch for snow that slides easily on a recently buried crust on southerly slopes or on any convex, unsupported terrain feature.

    Example wind slab.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    With lots of fresh snow over a crust, warming temperatures and a strong late February sun, wet loose avalanches could begin running naturally on Saturday. If the sun is out where you are, expect these to happen on steep slopes that face toward the sun during the middle of the day. Moist, sticky snow and rollerballs are good indicators that the snow is capable of producing these. Time your travels to avoid steep south facing slopes in the middle of the day to avoid getting avalanched by a wet loose slide.

    (3/8/2020) Example wet loose avalanche.

Avalanche Discussion

Observers at Blewett Pass on Friday found a couple layers of buried surface hoar stacked within wind slabs, 1ft and 2ft down, respectively. These were on both shaded and south facing aspects at about 5,800ft and produced clean, planer shears. An observer reported a very large avalanche that appears to have occurred on our mid-January crust from Manastash Ridge on the 24th, and on Friday snowpack tests on this layer near Blewett Pass showed that people can still trigger avalanches on it. About a foot of new snow had fallen by the end of the day Friday, and intense wind loading was observed near ridgetops in the zone. The new snow has buried recent sun crust on steep south facing slopes, and potentially another layer of surface hoar in some areas. You can find a thin melt freeze crust from the 22nd about a foot down at elevations up to 5,000ft.

From the 20-23rd a massive storm brought up to 6" of water equivalent to the mountains near the crest, but much less to the Wenatchee Range further east. Numerous deep, wide, and destructive avalanches ran on, or around the 22nd:

Dirty Face Mtn- both the SE and E faces produced avalanches to at least D3, running far down the mountain with some very deep crowns.

Round mtn- avalanches on SE aspect as well as a D3 avalanche on SW near 5,000ft on Nason Ridge to the west of Round Mtn.

Tumwater Canyon-  Avalanches ran on NE-SE with numerous loose wet to size D1-2 and a few slab avalanches to D2.5. 

In the Icicle drainage:

Sixty-six Hundred Ridge- An avalanche on NE, 6600ft ran size D3, R4 and took out trees

Big Slide creek- A SE aspect above treeline. Size D3.5-4

Mt Cashmere- Above the Eight-mile trailhead.  7,000ft, SSE. D3.5-4

Regions covered