Lawinenlagebericht

West Slopes North

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Expect more snowfall, strong winds, and dangerous avalanche conditions, especially in the afternoon. With continued snowfall and wind-loading building a slab over a known weak layer, it would be wise to stick with conservative, lower-angled terrain. Stormy conditions should make navigating and assessing avalanche terrain quite difficult by the end of the day.

Lawinenprobleme

  • Storm Slabs

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

    Over 1’ of new snow accumulated in most areas, and there is more on the way. Wind-drifted areas had depths of 2-3’. More importantly, observers reported a handful of small but remotely triggered avalanches that failed in a layer of buried surface hoar. 

    While this may not be a problem in all areas of West North, it should be on your radar no matter where you head on Monday. Avalanches that fail on surface hoar can be triggered from the middle of a slope, from flat terrain below a steeper slope, or remotely. The crowns can also wrap around terrain features.

    You are more likely to trigger an avalanche on wind-loaded slopes but consider all steep slopes suspect until proven innocent. Don't ignore signs of instability like whumphing or shooting cracks. When in doubt, stay on slopes to low in angle to slide. Hand shears and other simple tests can help you evaluate layers near the surface, but you will need to dig down to look for surface hoar. 

    (3/10/2024)

    The crown of a remotely triggered avalanche above Upper Bagley Lake. It failed in a layer of surface hoar that was likely buried on March 8th.

    (SS-ASr-D1.5-I)

    Photo: Zack McGill

Avalanche Discussion

NWAC will be closed on Tuesday, March 12th, as we gather and grieve following the death of one of our forecasters, Matt Primomo. We will not issue regular avalanche or mountain weather forecasts on Tuesday. We will return to normal operations on Wednesday, March 13th. We appreciate the community's understanding and support during this time.

Discussion:

Sunday yielded a variety of observations depending on your location in the forecast zone.

Observers in the Baker BC reported small but remotely triggered avalanches, wind-drifted snow, and generally stormy conditions for most of the day. In addition to reported avalanches in Swift Creek and Bagely Basin, avalanche control work in wind-loaded terrain produced slab avalanches to D2 in size. Another avalanche was reported from Shuksan Arm, but it’s unknown if it was natural or remotely triggered by people on the ridge above.

An NWAC Forecast team in Glacier Creek found evidence of buried surface hoar and plenty of wind-drifted snow. Still, no avalanches were observed despite plenty of people traveling on short, steep slopes at mid-elevations. Thick pillows of wind-drifted snow could be found alternating with areas where the new snow was nearly blown off down to the old, slightly crusty surface. 

When it comes to buried weak layers, it seems quite common to have a wide variety of distribution across the various subzones of West North. This is due to differences in weak layer development and also weather factors that either preserve or destroy weak snow at the surface - facets or surface hoar, or even light-density stellar grains - before it can be capped and buried by additional snow. If you were to trigger an avalanche on buried surface hoar in the coming days, it would most likely be on mid-elevation shaded slopes where the surface hoar didn’t melt, and the wind didn’t blow it away. But it might be found in terrain with different characteristics as well. 

 

 

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