Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

New snow and strong winds will increase the avalanche danger on Sunday at mid and upper elevations.  Dangerous avalanche conditions will likely develop in all areas Sunday night with an increasing likelihood of natural avalanches.  Plan your trip so you can exit safely. 

Avalanche problems

  • Wind Slabs

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

    Ridgeline winds are likely to increase further Saturday night through Sunday as a storm approaches.  Expect deeper wind slabs to develop Sunday afternoon and night as a potent storm rolls into the region.  Plan to avoid steep lee slopes below ridgelines where you find firmer wind-pressed snow.  If you encounter red flags like shooting cracks, hollow snow, or observe natural avalanches, step back and choose more sheltered or simpler terrain.

    Tune into changing conditions as the day progresses. The new snow may bond poorly to underlying weak snow surfaces and avalanches may break wider than expected or be triggered on approach from below. 

    As conditions deteriorate further Sunday evening, large natural avalanches are possible.  Avoid prolonged exposure to runouts later in the day and plan your route so you have a safe exit.  

    (12/29/2021)

    Wind slabs like the one in the photo from Delancey Ridge on the 29th may grow large by the end of Sunday.

    Photo: Will Govus

Avalanche Discussion

Several small natural wind slab avalanches were reported throughout the week, including Saturday, as moderate ridgeline winds easily moved low-density snow and formed shallow wind slabs below ridgelines.  Small loose dry avalanches or sluffs were easy to find in steep wind sheltered terrain.  Professional and public observations noted surface hoar on many aspects in the Hairpin Valley up to 7000' in elevation.  With this storm cycle just beginning, we'll see if this becomes a player over the coming days.  While this should be a cold storm, new snow will layer up over weak surfaces.  Storm slabs will likely come into the picture Sunday night when higher snowfall rates and snow totals are expected.  It's not time to shed those extra layers yet, the East North will stay cold over the next few days with temperatures in the single digits and teens. 

At the interface that was buried around the solstice, observers reported finding surface hoar as well as a thin sun crust on steeper S-SW slopes.   While no recent avalanche activity has been observed down to these layers in this zone, further west in the Mt Baker backcountry, a deep persistent slab up to 5' deep released sometime on 12/31 on surface hoar buried above the solstice crust.  Other avalanches down to this interface have released infrequently over the past week on the west side of the Cascades. Keep this in mind if you push to the western boundaries of the zone such as near or west of Rainy Pass where we know less about the snowpack. 

The last widespread avalanche cycle occurred on Saturday, Dec 18th (up to size D2.5) in the Washington Pass area.  A crust buried in early December can now be found roughly 4-5 feet below the surface, especially on slopes near and above 6000 ft.  We don't know of any recent avalanche activity on this crust, but observers have noted weaker faceted grains (1mm) above it as recently as Dec 30th. If you get out, submit an observation and help contribute to the forecast. 

Happy New Year from all of us at NWAC!

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