Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Avoid all avalanche terrain due to very dangerous avalanche conditions near and above treeline as rain destabilizes and dense snow overburdens dry snow. Natural and human-triggered wet or dry snow avalanches will be large, widespread, and difficult to survive. Below treeline, choose forested areas and slopes less than 35 degrees that are not exposed to large avalanches from above.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    We're expecting a jump in snow levels from near pass level Tuesday night up to 6000-6500 ft for much of Tuesday with strong warming. This is a recipe for widespread natural Wet Loose  avalanche cycle as dry snow changes to rain and percolates into the upper snowpack. Dry snow destabilizes very rapidly when it becomes wet. The snowpack prior to the current storm cycle is consolidating and well set up to handle a load. Thus, we expect most avalanche activity to entrain the 6-24 inches of snow projected to fall from Monday onwards, with the largest and deepest avalanches at higher elevations where precipitation remains snow longer into the day on Tuesday.  If it is still snowing at any location, expect a transition to rain during the daytime that will create rapidly deteriorating avalanche conditions. Avoid anywhere that avalanches can start, stop, or run. At lower elevations, as rain continues to fall on the snowpack, boot penetration greater than 6" serves as a reminder that Wet Loose avalanches may be triggered on any slopes steeper than 35 degrees.

    Of the 4" of precipitation that falls during the next 24 hours, much of it will be rain below treeline. Glide avalanches will occur on smooth rock faces. Avoid travel on or under these features as these avalanches can be large and may fail anytime there is liquid water flowing beneath the snowpack.

    Example: Powerful Wet Loose Avalanche.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Near and above treeline, heavy dense snow will load lower density layers from earlier in the storm cycle, creating widespread slabs 6-24" deep that you can easily trigger within the recent storm snow. Given the heavy, dense snow these slabs will have plenty of force to harm or kill you. Firmer over weaker snow will confirm the very dangerous conditions. A rapidly ascending rain line early in the day may quickly confine storm slabs to above treeline areas. Keep things simple and avoid all avalanche terrain near and above treeline where slabs can start, stop, or run.

    Example: storm slab avalanche.

Avalanche Discussion

The Snoqualmie Pass area picked up 4-6" of snow with snow levels between 2500 and 3000 ft on Monday. We're expecting another 6-12" of snow above 3500 ft Monday night before a potentially rapid transition to rain late Monday night and early Tuesday up to the top of the near treeline band or even above treeline by afternoon. This transition will be very dangerous with widespread large avalanche activity that should keep you out of avalanche terrain. Below the new snow, NWAC professionals in the Stampede Pass area and several avalanche classes in the Alpental Valley over the weekend found a well-settled snowpack that keeps us focused on the snow falling within this storm cycle, although an isolated very large avalanche failing down to the January 1st crust is not out of the question.

Tuesday represents a drastic uptick in avalanche danger. Shallow wind slabs have been the story for the last several days. We received a few reports of small skier triggered wind slabs over the weekend.

Despite the generally deep and strong snowpack around Snoqualmie Pass, open creeks remain a significant hazard. Seek out safe crossings and give yourself extra time to navigate this non-avalanche hazard. 

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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