Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

It'll be another day to let the snowpack adjust before trusting steeper slopes. The mountains have just begun to shed their winter coats, and more wet loose avalanches could be triggered from steep slopes with saturated and punchy snow. The thaw may increase the chances of triggering large wet or persistent slabs on higher elevation, shaded terrain.

Lawinenprobleme

  • Loose Wet

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

    Recent snow is still in the process of transitioning to wet snow at upper elevations, and near the crest. A warming trend should begin to wind down (for the time being) later in the day on Wednesday, but until that happens wet loose avalanches will remain possible.  Signs of wet loose avalanche activity are rollerballs, fresh fan-shaped avalanches with chunky-looking debris, and sometimes you can hear them. If you can sink in deeply into wet snow, steer around large steep features.

    Natural wet loose avalanches are not expected, but you could trigger them on steep slopes. At upper elevations, wet slides could entrain lots of snow and become large avalanches. They could also pull out wider slab avalanches on deeper layers. Above 5,500ft, NW-NE aspects harbor weaker, faceted grains over a crust from early March. This layer could be down close to 3ft deep in some areas, and any avalanche that runs on it would be very large. There is uncertainty as to how the snowpack is adjusting, so keep an eye and ear out for signs of current activity.

    Example large wet loose avalanches. Photo: Matt Primomo

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    A pronounced thaw may be increasing the chances of triggering a persistent slab. Observers have reported some whumphing collapses, and one ski triggered avalanche 2ft deep last weekend. These are all direct signs of instability relating to a layer of faceted grains overlying a crust buried in early March. However, many observers reported a lack of whumphing collapses, but still found the weak structure in profiles. This insight is unsettling, because it means you may not get direct feedback before triggering a deeper slide.

    Any avalanche that runs on the crust could be a couple feet deep and could be fairly wide. Avalanches could be triggered from a distance, or below.  Plan to stay off of large and steep, shaded slopes above 5,500ft, especially if they appear to have been loaded by the wind in recent days or if the snow is wet and punchy. Travel on lower angled slopes, without large steep features above you. Large loads like cornice failures or snowmobiles could initiate persistent slabs more easily.

    Example recent slab avalanche from the East South zone.

    Photo: Andrew Kiefer

Avalanche Discussion

The warmup is on, and the mountains have just begun to shed their winter coats. Temperatures climbed high on Tuesday, with the top of Dirtyface hitting 46 F, and Blewett Pass hitting 56F. Forecaster Katie Warren observed 4-6" of recent snow over a crust on Dirtyface on Tuesday, with snow that was not yet fully transitioned to spring like snow. Monday's warm front dropped about 0.5" of SWE at Sasse Ridge Snotel site and 6" of new snow. Higher elevation locations near the crest likely received closer to a foot of new snow since the 20th. Large wet loose avalanches were observed at high elevations of the Chiwaukums, Stevens Pass, Snoqualmie Pass and the warming likely affected snow surfaces even on the highest, shadiest faces of the range. 

Observers have been documenting weaker, faceted grains and/or surface hoar overlying a crust from early March on W-N-E aspects from Stemilt Basin to Icicle Creek, and other areas to the north and south. Above 5,500ft, these slopes harbor weaker, faceted grains over a crust from early March. This layer could be down 2ft deep or greater in some areas. On Sunday, skiers triggered an avalanche on it near Mt Fernow that was 2ft deep and 40ft wide. Observers in the Chiwaukum range also found the weak layer above 5,000ft and reported significant wind loading on Saturday. On Friday, I found the March 8th facets in the White Pine drainage. A vague observation of large collapses in the Teanaway also came in from Saturday (unknown details). 

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