Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
4 · Gross
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Expect a very stormy day, and increasing danger as you gain elevation. The west half of the zone is expected to receive much more snow than further east, and these upper elevations may become very dangerous by afternoon. Slides may break widely on buried crust and facet weak layers 3ft deep, so it'll be a good day to stick to lower elevations and lower angled slopes away from larger features. 

Lawinenprobleme

  • Storm Slabs

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

    As snowfall increases during the daytime, storm slabs should become more reactive. The west half of the zone is expected to see higher snow totals, so this is where the storm slabs should form. These could break within the storm snow, at the old snow interface, or even deeper on a number of weaker layers. The new snow has recently buried a layer of facets and surface hoar. As such, slides may fracture widely and could be triggered from adjacent slopes. Above 5,000ft slides could run on more deeply buried weak layers including weak snow and a crust from early February, so slabs could break over 2.5ft deep in places.

    With these dangerous conditions and snowpack complexity, it'll be a day to keep things simple with your terrain if you venture into the backcountry. Avalanche danger is expected to continue increasing into the overnight period, so it won't be a day to hang it out there. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2–3

    Strong westerly winds have been blowing since Friday afternoon, and should peak on Sunday. As new snow falls, wind will quickly transport it into thicker and stiffer slabs on high, exposed slopes. Its not just the new snow we're concerned about, its the weaker structure below that should start to get overloaded. In wind loaded areas, slabs may break over 3ft deep on layers of facets and crusts from earlier in the month so you won't want to mess with them.

    Stay off of and out from underneath large steep slopes at mid and upper elevations while this storm plays out. These types of avalanches may fracture widely across terrain features and could be triggered from adjacent and lower angled slopes. 

    Large natural avalanche that ran on the early February Crust in the Teanaway on Feb 18th. This same layer is still active and we're likely to see more avalanches run on it.

    HS-N-R3-D2-I

    Photo: Katie Warren

Avalanche Discussion

Sunday should be a very stormy day wherever you go. However, you'll find a gradient with both elevation and from west to east in the range. The higher you go, the colder it'll be and the stronger the winds will blow. We're likely to see rain below 4,000ft, so keep wet avalanche problems in your mind at those elevations. Areas further west in the range stand to pick up over a foot of new snow, while areas further east may only get a few inches. 

Our snowpack has become complicated over the course of intermittent dry spells in February. There are multiple potential weak layers in the snowpack, all the way down to the early February Crust. This crust may be up to 2ft deep in some areas, and it'll be getting buried deeper on Sunday. There are also potential layers of surface hoar and faceted grains from the 11th, 14th, 18th, and the 24th. The upcoming storm and stormy week should begin to test all of these weak layers.

On February 22nd, a party of skiers in the Teanaway drainage triggered a slab avalanche on a layer of 1-2mm facets just above the early February crust. The large (D2) avalanche occurred near Longs Pass, on a W aspect at 6,200ft. It was triggered from a lower-angle, 30-degree slope near a cluster of trees. A crack propagated uphill and across in both directions. The avalanche ran to either side of the lower-angle feature and didn't involve the party that triggered it. This is a good example of the types of slides we're likely to see more of this week.

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