Avalanche forecast

East Slopes North

Northwest Avalanche Center
View on map

Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You may trigger shallow new wind slabs near and below ridgelines on Sunday.  Small loose wet avalanches are possible on very steep sunny slopes.  The low-likelihood/high consequence deep persistent slab threat may be easier to trigger in the Hart's Pass portion of the zone. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Up to a few inches of new snow along with moderate winds at upper elevations are expected Saturday night.  Use caution before engaging with steep open slopes below ridgelines where you find winds have drifted fresh snow.  The new snow may bond poorly to steep slopes with a sun crust of varying thickness or to shady aspects at higher elevations with weak faceted snow.   Look for cracking in the new snow and check the bonding of the new to old snow interface on small test slopes.  

    The sun should make an extended appearance tomorrow.  While the day may not be full-on bluebird, mid-March sunshine following fresh snow means small loose wet avalanches are possible on very steep sunny slopes.  Also watch for small natural loose wet avalanches that can release below rock faces that heat up quickly. 

    While any type of avalanches within the new snow should be small, think about avoiding terrain where small avalanches within the new snow may overlap with the deep persistent slab problem. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    While it's unlikely you'll trigger a deep slab avalanche in much of the zone, however, you may be more likely to trigger one near Harts Pass or other locations where the weak layer is less than 3 feet below the surface.  What can you do to manage this low-likelihood/high consequence problem?   You can limit your exposure to large start zones and very steep slopes, especially those with big overhanging cornices (see photo).  Also, avoid complex and unsupported terrain, shallow, rocky areas, and unsupported slopes.  The bottom line with these avalanches is while there are unlikely, you should assume they'll be large enough to kill you.  

    On March 3rd and then again on the 9th, backcountry travelers in the Harts Pass area triggered large to very large avalanches on northerly aspects near treeline.  A cornice-triggered avalanche may have also occurred around the 8th or 9th on McGregor Mtn. You can find the late January weak layer (facets sandwiched between two crusts) 3-5' below the surface. Snowpack tests can help you identify the layer of concern. Observers continue to report sudden or propagating test results even as avalanches have become difficult to trigger. East of Washington Pass, the snowpack becomes shallower, and this interface may be nearer to the snow surface.

    (3/10/2022)

    In the center of the photo is a recent D2.5 deep slab, likely triggered by a cornice fall. 

    To the right of the photo, you can see a similar-sized avalanche that likely occurred during the natural cycle of 2/28-3/1.

    McGregor Mtn, NNE, 7,200ft.

    Photo: Matt Primomo

Avalanche Discussion

Saturday night will be the opening salvo as we enter a wetter pattern.  Precipitation forecasts are uncertain, but we are entering a more active weather pattern that will test deeper weak layers in the snowpack. 

On March 9th, observers near Harts Pass remotely triggered a large, R3-D2 avalanche from 20-30 feet away. The avalanche occurred roughly around 6,600ft on a north aspect and failed on facets above a crust.  However,  a crown profile revealed a uniquely shallow snowpack suggesting previous avalanches may have already occurred on this interface. 

On March 3rd, a size D2.5 avalanche was triggered nearby on Tatie Peak on a northeast aspect at 6,800ft. Fortunately, no one was caught in these avalanches. Another avalanche likely occurred on the late January weak layer with cornice fall around March 8-9th on McGregor Mtn, NNE, 7000ft. Observers reported other deep crowns in the Hairpin Valley and near Azurite Pass after a widespread avalanche cycle on 2/28-3/1. This is evidence that the late January facets could produce more avalanches under the right conditions.

Travel conditions may be challenging, especially at lower elevations where you'll find plenty of firm avalanche debris and firm crusts following the 2/28-3/1 cycle. The rain formed a crust up to 5,500- 6,500ft depending on the location in the zone.  

Regions covered