Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

A strong storm will bring snow, strong winds, and increasingly dangerous avalanche conditions on Wednesday. You could easily trigger large avalanches in steep terrain, particularly in areas exposed to winds. Avoid steep slopes and seek out low-angle terrain sheltered from the wind.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2

    Strong winds and a significant storm will impact the Cascades on Wednesday. Expect peak precipitation to occur during the day, with increasing wind speeds. Plenty of snow is available for transport, and the storm will bring plenty more snow over the Cascade crest to the east slopes of the Cascades. Winds are forecasted to bump up to over 40mph in the afternoon and will easily drift snow around, even at lower elevations. So any steep open terrain will potentially harbor large wind slabs. While the storm pummels the mountains, avoiding steep, wind-exposed terrain at all elevations will be best. But avoiding these wind slabs in alpine terrain will be especially challenging. Simple, low-angle slopes will be the best option to reduce to likelihood of triggering an avalanche. The most likely places to trigger these avalanches will be steep slopes below ridges, steep convex rolls, and the base of cliffs. Feel for stiff over soft snow layering and look for signs of cracking or collapsing to identify and avoid areas of unstable wind-drifted snow.

    (2/27/2023) Cracking in wind drifted snow. Photo: Katie Warren

  • Storm Slabs

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

    This powerful storm will bring significant snow totals to the east slopes, particularly near the Cascade Crest in areas like Salmon La Sac, Holden, and the Upper Icicle Drainage. You should also expect to find reactive storm slabs on steep slopes in sheltered areas. New snow will accumulate over slick crusts on southerly aspects and weak surfaces on northerly aspects, so reactivity of the storm slabs could vary significantly with aspect. Watch for signs of instability, such as shooting cracks, collapsing, and recent avalanches, as red flags to avoid steep terrain. You can use small, inconsequential test slopes and quick hand pits to observe how the new snow reacts. Avoid steep terrain if you find the new snow sliding easily or test slopes producing mini avalanches.

    (12/20/2022)

    These small test slopes are excellent indicators of unstable storm slabs.

    Photo: Public Observation

Avalanche Discussion

An area of convergence is likely to setup near Stevens Pass, potentially shifting around toward Snoqualmie. In areas like Salmon La Sac, Holden, and Wenatchee River Drainage, the spillover from the convergence zone could bring heavy snowfall with very high precipitation rates. Snowfall rates of more than an inch an hour are possible and may quickly lead to deteriorating stability. So stay tuned into the weather as this storm develops, and be prepared to dial back terrain choices. The combination of heavy snow and strong winds may lead to a small natural cycle during the day, so as you plan your day consider the consequences of overhead hazards and terrain traps. Areas of the forecast zone further east may pick up less snow than locations closer to the crest. 

Observers in the Icicle Drainage on Wednesday reported wet, heavy snow on southern slopes and some small natural wet loose avalanches. These slopes will refreeze overnight, creating a slick crust that could be a potential bed surface for avalanches with the incoming storm. They also observed wind-affected surfaces and wind transporting snow along ridgelines and small wind slabs from the previous 12-24 hours. 

You can find 1-3ft of newer snow from the past week sitting over a crust from Valentine's Day, which often presents as a crust/facet sandwich, with weaker snow beneath the upper crust. Observations indicate quite a wide variability in the structure of this layer. Still, over the weekend, observers reported some whumphing collapses and a propagating test result below this crust in the mid-Icicle drainage. We have yet to observe avalanche activity on this layer but continue to monitor it as snow adds up. If you get out into the mountains, submit an observation to share what you found.

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