Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Steer around wind-drifted piles of snow on Tuesday where you could trigger an avalanche more easily. The snowpack may still need some time to come to grips with the large amount of water we just received, so make conservative terrain choices. If you travel to elevations that did not see rain over the weekend, expect larger and more dangerous avalanches.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    The wind may have been transporting snow above the rain/snow line these past few days at Snoqualmie Pass, building dangerous Wind Slabs in these areas. As temperatures begin to cool and snow levels drop Monday night into Tuesday, expect gusty conditions to continue to transport snow at multiple elevation bands, thickening those existing slabs while building new ones in areas that previously did not see snow. Take a look for blowing snow, fresh cornices, textured surfaces, or smooth pillow-like piles of snow to help you determine where Wind Slabs could be developing. Wind Slabs often develop on leeward slopes, at the base of cliffs, or on the sides of gullies, so give these areas extra attention. If you experience clues of unstable snow such as shooting cracks or whumpfing collapses as you travel, steer around slopes greater than 35 degrees.

    (12/18/2020) As of Saturday afternoon, there was roughly a meter of snow over the 12/9 crust at middle and upper elevations at Snoqualmie Pass. Above the rain line, this slab has only thickened due to snow and wind.

  • Wet Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2

    Although unlikely at this point, we’re going to continue to be concerned about Wet Slab avalanches for another day at Snoqualmie Pass. It can take some time for water to percolate through the snowpack and weaken the bonds between snow crystals, releasing large natural avalanches, so let’s give the snowpack some more time. Since wet avalanches are not well understood and the timing of wet avalanches is very difficult to predict, they can act in surprising ways. You can mitigate this uncertainty by minimizing your exposure through the selection of safe travel routes, staying off slopes over 35 degrees, and being aware of the terrain above you at all times. 

    (12/21/2020) This Wet Slab avalanche in the neighboring West South zone was found at Paradise. It connected terrain features for over 200 yards in width with a crown depth between 1 and 2 feet.

Avalanche Discussion

We are still lacking information about if a large natural avalanche cycle has occurred at Snoqualmie Pass since Saturday, but our best guess is that it has. The neighboring zones of Stevens Pass and the West South have both had notable avalanche cycles over the past two days, with some slides being estimated as D2.5 with 3-foot crowns. There were numerous D2 slides found in the Paradise area on Monday with 1-2 foot crowns that propagated widely and connected terrain features. This comes a day after a similar cycle was observed in the Crystal backcountry. Snoqualmie Pass did not receive quite as much water as Paradise, but did have a similar snowpack structure going into the storm on Saturday. The limited observations we do have from the zone continue to point to weak layers within the snowpack that are capable of producing large slides given the right conditions. Have these conditions already been met or are we still playing the waiting game? The cooling temperatures should help to stabilize the snowpack overall, but ease into terrain carefully on Tuesday and take note of how much new snow has been building up. If new snow fell on a frozen surface, we could be talking about smaller, but reactive avalanches in the new snow. Above the previous rain/snow line, any avalanches will be much larger, and being caught in one would have serious consequences.

Below the rain/snow line,  challenging travel conditions may be found. Anticipate open creeks, thin coverage, and plenty of obstacles to navigate. 

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.

Régions couvertes