Lawinenlagebericht

Snoqualmie Pass

Northwest Avalanche Center
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Lawinengefahr

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

The danger rating is on a downward trend because naturally triggered avalanches are expected to slow on Wednesday. However, the threat of human triggered avalanches large enough to bury and kill you should steer you toward slopes less than 35 degrees. Avalanches need to be on your radar anywhere you are sinking into the snow more than a few inches, whether the snow is dry or wet.

Lawinenprobleme

  • Storm Slabs

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

    Snoqualmie Pass has had almost continuous precipitation since Monday morning in the form of both rain and snow. This has essentially created two elevation bands, delineated by the rain/snow line. As you ascend in elevation above this line, expect to find colder, drier snow and dangerous Storm Slabs. These slabs should be large and could be very large in isolated areas, particularly if strong winds on Tuesday night are able to redistribute the snow into thicker slabs on leeward slopes. We are most concerned with new slabs formed the past few days having a poor bond to the old snow surface (1/11 interface) as well as interstorm layers within the slab. Take some time to investigate these bonds and how much snow makes up any potential slab. You can use test slopes or hand pits as you travel to give you an indication of slab potential and its reactivity. If you find a poor bond, see other avalanches, or find heavy snow over weaker snow, avoid all avalanche terrain where avalanches can start, run, or stop.

    (1/7/2021) This large crown on Chair Peak occurred during a previous storm cycle, but we wouldn't be surprised to find similar avalanches once we get some visibility around the zone.

  • Loose Wet

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

    Below the rain/snow line, you should find much different conditions. The rain produced a widespread natural avalanche cycle on Tuesday and we expect that to continue on Tuesday night. As temperatures cool and the bulk of the precipitation exits our zone, natural avalanches should taper on Wednesday. That’s not to say we’ll be home-free. Even with decreased likelihood, the snowpack still needs time to adjust to all the recent rain and may still be capable of producing surprising wet avalanches, especially earlier in the day. 

    Although listed as Wet Loose, other wet snow related avalanches such as Wet Slab and Glide are still on our minds and these problems are often intermingled. Wet Loose avalanches often start at a point and are capable of entraining lots of snow, triggering slabs, and traveling far distances as they descend. Rollerballs, pinwheels, and fan-shaped avalanche debris are signs of wet loose avalanches. If you notice these signs, steer around terrain features greater than 35 degrees and avoid terrain traps such as creeks, gullies, or cliffs. Anywhere you find unconsolidated wet snow, be leery of traveling on steeper slopes and avoid traveling underneath steep rocky slopes and cliff bands where snow could shed from above.

    (12/19/2020) This is a small Wet Loose avalanche (D1) from earlier this season. Look for fan-shaped debris and avoid steep slopes above you as you travel.

Avalanche Discussion

As of Tuesday afternoon, around 4 inches of water has fallen at Snoqualmie Pass since Monday morning. Starting as all snow, before switching over to rain at lower and mid elevations, natural avalanches were easy to predict and confirm with limited observations on Tuesday. Alpental Pro Patrol was able to identify multiple natural Storm Slab avalanches from the cooler part of the storm before confirming Wet Loose avalanches after the onset of rain. As we extrapolate that data into other parts of the zone, we can be confident that widespread naturals did occur on Tuesday and feel confident that there will be more naturals on Tuesday night as more precipitation and rising freezing levels impact the zone. If this additional water and warmup were to be occurring during our forecast period, we would continue to be at High avalanche danger. However, by daybreak on Wednesday, the bulk of precipitation should be done with, and freezing levels should be lowering, finishing this wet couple of days with cooling temperatures to help us on our journey to better stability than we have seen recently.

This doesn’t mean that you should let your guard down on Wednesday. We just received a lot of water in a short period of time, and the snowpack does not like rapid change. Avalanches on Tuesday were large to very large (D2 to D3), and although the natural cycle may be coming to a close, human triggered avalanches of the same size are expected on Wednesday. The snowpack still needs time to adjust to the large volume of water it recently received. As temperatures cool and the snowpack starts to freeze from the surface down, remember that it can take some time for water to percolate through the snowpack. Surprising wet avalanches can still occur hours after rain has stopped. Elevations above the rain/snow line should hold significant snow totals and could produce very dangerous avalanche conditions, ease into terrain and stay off slopes 35 degrees and steeper. At lower elevations, rain effects may be significant, with open creeks, collapsed snow bridges, and heavy wet snow. Additionally, trees have been breaking and significant loads have been falling out of the trees, creating a dangerous travel hazard in forested areas.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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