Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Dangerous avalanche conditions are expected on Tuesday as the bulk of this dynamic storm takes aim at Snoqualmie Pass. Stick to conservative terrain by avoiding slopes over 35 degrees or wind-loaded areas where triggering an avalanche is more likely.  Natural avalanches will be more likely during periods of heavy precipitation or wind.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Continued snow and increasing winds will only thicken existing Storm Slabs around Snoqualmie Pass on Tuesday. These slabs should be larger as you ascend in elevation above the rain/snow line and in wind-loaded terrain. You can use quick hand pits, small test slopes, or uptrack tests to gather information about slab potential and points of weakness in the upper snowpack. With several rounds of precipitation and fluctuating freezing levels during this storm, there could be multiple interstorm layers to check for heavy snow over weak snow. You're also going to want to check the bonding to the previous surface. You may be able to trigger an avalanche on any slope over 35 degrees or in wind-loaded terrain.

    On northerly aspects at upper elevations, some weak snow above the Early March Crust could come into play, allowing slabs to break in surprising ways and span far distances. You can get more details about these persistent grains in the discussion below.

    (3/13/2022)

    Very small natural storm slab avalanches Sunday (3/13) on the north slope of Chair Peak. Notice these slides all occurred on very steep convex rollovers. 

    Photo: Shane Robinson

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Lower elevations have seen several rounds of rain recently and should be well suited to handle more. That said, the dynamic nature of this storm and fluctuating freezing levels means that we can’t rule out the possibility of a lingering wet avalanche. You should be able to tell where the rain/snow line is by looking for wet and sticky snow or existing snow in the trees. Below this line, keep an eye out for new fan shaped avalanche debris or fresh rollerballs during your travels to help indicate another round of wet avalanches are possible. Any potential wet avalanche should occur on steep slopes and be relatively small. That said, they can be powerful and you don’t want to get caught off guard by one near terrain traps such as cliffs or open creeks. 

    (3/6/2022)

    Example: Our last atmospheric river event produced a mix of slabs and loose debris throughout the Snoqualmie Pass zone.

    Photo: Andy Harrington

Avalanche Discussion

After receiving around an inch of precipitation on Monday, the storm is set to deliver its largest wave of snow and rain to Snoqualmie Pass on Monday night into Tuesday. Although considered a weak atmospheric river by many, this is a strong storm more in line with what we often see in the Cascades. We anticipate that a natural avalanche cycle will occur overnight during the height of precipitation intensities. On Tuesday, temperatures should slowly cool and snow showers should become more showery throughout the day. The question mark will be the timing of the transition between these periods. If you find that heavy snow is still falling in the morning, there may be an increased likelihood of natural avalanches and potentially very dangerous avalanche conditions. Strong winds and continued precipitation throughout the day on Tuesday could revitalize natural activity or reload slopes that have already slid. Choose terrain carefully and give the snowpack time to adjust for duration of this storm. 

The Late March Crust is a prominent snowpack marker that should be the baseline for any snowpack tests you perform on Tuesday. All of the snow above it is in play for avalanches during this storm, and avalanches have the potential to run far distances on this firm bed surface. On upper elevation northerly slopes, we have been tracking some weak snow (facets) just above the Late March Crust. If you find these persistent grain types, avalanches could act in surprising ways by connecting terrain features, spanning far distances, or breaking above you. They could even be triggered from far distances in isolated locations. Many small storm slab avalanches were observed on convex northerly slopes on Sunday before this storm started to really impact the zone. These small slides may have been a precursor of things to come.

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