Lawinenlagebericht

West Slopes North

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

A storm cycle gains momentum on Thursday with cooling temperatures increasing slab size and distribution at middle and upper elevations throughout the day. Use small test slopes to gauge the reactivity of storm snow and the bond to a stout melt-freeze crust before venturing onto slopes steeper than 35 degrees. If the crust remains poorly bonded or the winds transport significant amounts of snow in your terrain, seek simple, supported slopes.

Lawinenprobleme

  • Storm Slabs

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

    Most likely, you will find the moist snow from Wednesday bonding well to the underlying crust with slab hazard building within the expected 6-8" of storm snow arriving Wednesday night through Thursday. This may be just enough snow to produce mostly small slabs within layers that form during periods of higher snowfall intensity. Wind drifts could form slightly larger slabs (to size 1.5) on the northern half of the compass. If wind speeds exceed forecast amounts, these slabs could become large by the end of the day. Steer around steep slopes and start zones with 8" of dry snow.

    The less likely scenario is that the new snow insulates the poorly bonded crust and that snow remains reactive down to the crust. If this scenario plays out, reactivity would be more widespread and slabs could be large, breaking below the moist snow layer. Take your time to give representative test slopes a stomp and try to initiate some shear on top of the crust to see if this alternative scenario remains in play. In this case, you'll want to avoid all slopes steeper than 35 degrees until the reactive interface gains strength.

    Example: You can trigger a soft slab avalanche like this one on a steep or poorly supported slope on Thursday.

    Photo: Irene Henninger

Avalanche Discussion

Backcountry travelers and Baker Pro Patrol reported a poor bond between the 4-6" of snow that fell Tuesday through Wednesday and the crust that formed from last weekend's rain event. The culprit appears to be the shallow (4") snow that ended the weekend's storm as the underlying crust formed. That snow weakened under clearing skies at the beginning of the week with near-surface facets found on all aspects at 5000 ft. Backcountry Travelers reported The avalanches were shallow (6-8" deep), but were easily triggered by skiers or snow and also by snow falling off rocks and vegetation. These slabs didn't exhibit wide propagation but ran efficiently on steep slopes. Given the reported avalanche activity on Wednesday, it is likely that these weaker grain types were buried intact, but we don't know how long they will stick around or whether they will continue to be problematic. Given the uncertainty in the forecast, some extra caution is warranted. Ease into the terrain slowly taking cues from the slab character and any signs of cracking, whumphs, or recent activity that might give you clues regarding the layer in question. If snowfall amounts or winds exceed forecast numbers over the next 24 hours, dangerous avalanche conditions may develop and you'll want to reduce your terrain selection accordingly.

Observers found little in the way of wind slab on Tuesday. A few wind-loaded features would produce cracking and shed small blocks when kicked, but slab formation was too isolated to be a problem in the Baker Backcountry.  Further east in the zone, wind slabs were more reactive at middle and upper elevations in Sibley Creek where stronger winds were observed. It is likely that these slabs are quickly gaining strength given the recent mild temperatures.

Below the firm melt-freeze crust crust, all layers are well-bonded and consist of crusts, melt forms, or rounded grains. Snowpits at mid and upper elevations have repeatedly shown a well-consolidated snowpack with no layers of concern.

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