Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Tuesday is shaping up to be a dangerous day in the mountains with multiple and complex avalanche problems. Best to keep your terrain selection simple: Plan to avoid steep slopes near and above treeline as strong winds and heavy new snow could tip some slopes over the edge with large avalanches. Small loose wet slides could pose a danger at lower elevations as the daytime warms.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    We may end up with close to a foot of new snow at mid and upper elevations by Tuesday afternoon. In some areas, the new snow may bond well, but in others it probably won't. You could trigger slopes easily- potentially from a distance with your weight. Be especially careful on any upper elevation terrain facing northwest to northeast. This is where old snow is weakest; Where faceted grains rest above a crust from early March. The variable nature of faceted grains over a crust from early March should make for tricky conditions, where some slopes avalanche but others don't. This weak structure is thought to be most problematic in the mountain near the crest.

    Look for shooting cracks, and signs of recent avalanche activity. If you find any of these, or if you find weaker snow over a crust beneath the storm snow, don't trust steep slopes. Be sure to regroup well away from any steep slope above, and keep you slope angles down below 30 degrees to stay safe.

    (3/14/2022 Stevens Pass) Tilt tests were good at showing the poor bonding with the early March crust and weaker snow above. Blocks slid off easily with ligh tapping. Photo: Matt Primomo

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2

    Very strong to extreme westerly winds should ramp up during the day. We could see intense wind drifting of snow, so slabs could form and fail quickly. Look for visual clues such as wind texturing or direct observations of wind drifting snow. Slabs could be large and wide in alpine terrain. Steer clear of steep slopes near and above treeline if you observe these signs.

    Example wind slab. Photo: Andrew Kiefer

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    With daytime warming, expect small rollerballs or wet loose avalanches lower elevation slopes in areas with new snow. Wet sticky snow can also be a good indicator that you could trigger small loose wet slides. Use caution on steep slopes or underneath any large consequential ones if you find these signs.

    (3/14/2022) Small loose wet slide in motion. Photo: Matt Primomo

Avalanche Discussion

It's time to take a big step back in our terrain selection. There could be a natural avalanche cycle in the alpine overnight into Tuesday with heavy snow and very strong winds. This could involve both dry snow, and wet snow at lower elevations. Weak faceted snow, sometimes overlying thick crusts, has been documented on sheltered northern aspects near the crest of the East Central and neighboring Snoqualmie and Stevens Passes. This notoriously weak structure may persist and cause lingering instabilities after this storm passes.

On Monday, Forecaster Katie Warren traveled to Red Top Lookout near Blewett Pass, and wasn't able to find faceted snow over the crust from early March at elevations traveled (up to 5,300ft). Avalanche danger was minimal at the time, with potential for small loose wet slides. Further west and at higher elevations the snowpack is likely quite a bit different, with the weak structure described above. 

Various challenging surface conditions exist at lower elevations, such as shallowly buried avalanche debris, and thin snow cover. A widespread avalanche cycle occurred throughout the Cascades on the 28th-March 1st, and left plenty of large piles of debris to navigate. 

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