Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Avalanche danger will be the greatest in the morning and slowly decrease through the afternoon. Give big steep slopes plenty of room while temperatures cool, precipitation becomes lighter and the new snow stabilizes. You could see continued wet avalanche activity at lower elevations.

Lawinenprobleme

  • Storm Slabs

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

    Above the rain-snow line, there should be 1-2' of new snow, especially in alpine terrain. The likelihood of seeing a natural slab avalanche will decrease but conditions will still be quite dangerous to start the day. 

    You might find shallow slabs that are reactive to the weight of a single person on steep slopes. These could even build through the day with light snowfall and wind speeds strong enough for snow transport. The bigger concern is thick slabs of dense new snow. They are often difficult for a person to trigger but produce destructive avalanches when provoked by a smaller loose snow avalanche, falling cornice, or some other sizeable trigger. 

    The best bet will be to just avoid traveling on or under big, steep slopes. Smaller bites of avalanche terrain might be reasonable in the second half of the day as the new snow stabilizes with a cooling trend. The usual tests for assessing new snow stability (test slopes, etc.) will be useful to get a read on shallower slabs found in the upper layers of new snow. The same tests don’t say much about the bond of a thick new snow layer to the old surface below.

    Large slab avalanche triggered by cornice fall during a rain event in the spring of 2022. Rain rills are visible on the snow surface lower on the slope.

    Photo: Julz Holder - Grounding Truth

  • Loose Wet

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

    While the bulk of the wet avalanche activity should occur overnight, danger from cornice falls, wet loose, glide and wet slab avalanches will persist. Friday won’t be the kind of day where you will be looking for rollerballs and other signs of instability to figure out when to move away from steep terrain. All the signs should be there in the morning - it’s just a matter of staying out of the way. Avoid traveling below glide cracks, sagging cornices, and other terrain features that routinely produce wet avalanches.

    Example of wet loose avalanche activity from a rain event in 2019.

Avalanche Discussion

The approaching storm ended up moving in a bit behind schedule Thursday. West Central saw only a trace of precipitation. Many weather stations around the zone showed high temperatures in the low 40s, but temperature alone was probably not enough to have a significant effect. In West North, a mix of rain and snow dribbled in through the afternoon and the first precipitation measurement with greater than 0.10”/hr didn’t occur until 5:00 pm at the Heather Meadows weather station. Stevens and Snoqualmie Pass also received a trace of precipitation.

Water amounts overnight - 0.75” of precipitation as snow above 5000’ and rain below - are still on track to have an effect on the not-very spring-like snowpack found across most of the Cascades. The heaviest precipitation should end by morning and be accompanied by a drop in snow levels. But it turns out mountain storms don’t read weather forecasts - be ready to change plans and expect higher danger if heavy rain or snowfall, or strong winds persist into the afternoon.

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