Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
1 · Gering
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 2 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Apart from shallow sluffing, triggering an avalanche is unlikely today in the Northwest Mountains.  Stay alert for isolated exceptions in wind-affected terrain: lingering thin wind slabs or a much larger avalanche that breaks on old weak layers on a slope with shallow and variable coverage.  Travel on slopes where the snowpack is consistently deep (more than 6 feet) and uniform for the safest riding. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    In the Northwest Mountains, high-consequence slabs breaking on older weak layers have become isolated and difficult to trigger. Persistent slabs are most likely triggered from an unusually shallow or previously wind-eroded slope where the total snowpack height is below average, or from random cornice falls. Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.  The most problematic structures are on shallower slopes on the north half of the compass.  Mid to low-elevation, southerly aspects have the most trustworthy snowpack.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem when in doubt.  

    The crown of a very large persistent slab remotely triggered by snowmobiles on March 8.  This slope is west facing and eroded by seasonal winds, making for a shallower and more problematic snowpack than other slopes. 

Avalanche Discussion

Wind transport has largely ended after easterly winds peaked on Thursday and Friday.  Most of the shallow wind slabs that formed earlier this week (ex. 1, ex 2) have healed up by now.  Isolated exceptions may exist on very steep or heavily drifted features.

The big news comes from the dramatic display of our persistent slab problem out of the Terminator Chutes yesterday evening.  The slab broke on basal weak layers on a seasonally shallow northwest-facing slope that likely saw some wind loading earlier this week from abnormal winds.  It looks like it might have been triggered naturally by a period of solar warming, or maybe it was Zane saying hello 9 years later.  Regardless, the shallow and variable snowpack in Terminator 3 has all the ingredients to stay away from today. This recent large avalanche near Copper Creek further illustrates the problem.   Our fieldwork yesterday demonstrates how slopes with a deeper snowpack are relatively stronger and more trustworthy.  This is why the deeper snowpack of the Northwest Mountains is at Low danger today.  You can significantly reduce the risk of triggering a large avalanche by traveling where the snowpack is consistently deeper than about 200 cm (~6 feet), or by traveling on slopes with thick, supportive crusts near the snow surface (most commonly on the southern half of the compass). 

CBAC Event:  The 50th Al Johnson Race is today! It's not too late to sign up. Last-minute registration and mandatory bib pickup are 9 a.m. to 11  a.m. at the Treasury Center.   Race starts at 1 p.m. at the bottom of the North Face Lift.  Party and awards at Butte 66 at 3:30.  All proceeds to benefit the CBAC.

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