Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Another round of moderate snow and wind will keep the avalanche danger elevated on Thursday.  Continue to avoid big open slopes where winds have drifted new snow over the last 2 days.   Below treeline you may encounter storm slabs on very steep rollovers and unsupported terrain features. 

Avalanche problems

  • Wind Slabs

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

    Storm totals from Tuesday night through Thursday afternoon should approach 12-18" with periods of moderate to strong SW ridgeline winds.  This isn't an epic storm cycle, but there are enough weather inputs to warrant conservative travel. 

    As you gain elevation and change aspects, look for visible clues of where winds have drifted snow.  You're most likely to trigger a slab avalanche just below lee ridges and other wind-loaded terrain features like at the base of cliffs.  Other red flags include shooting cracks through the snow and recent avalanches on similar slopes.  

     

    (12/19/2021)

    A crown from an avalanche (size D2) near Stevens Pass. This ran on 12/18 in wind affected terrain. Above treeline, NW, Chiwaukum range

    Photo: Matt Primomo

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Shallow storm slabs may form Thursday with another 5-9" of snow forecast. Storm slabs may fail either on the previous snow surface or within new storm layers.  You can easily assess this avalanche problem with quick snow pits or by testing inconsequential slopes.

    Surface hoar was reported in valley bottoms in the Washington Pass area prior to this storm cycle.  If you hear audible whumpfs while traveling below treeline, you may encounter avalanches that break wider than expected and are as deep as the two-day storm totals.  Adjust your terrain selection accordingly by choosing mellower terrain not connected to larger open slopes. 

    (12/20/2021)

    A storm slab avalanche that released on the 18th on a northerly aspect in the Hairpin valley. You could encounter similar slides on Thursday.

    Photo: Adam Butterfield

Avalanche Discussion

A few reports from the Washington Pass area noted the 6-10" of new snow was not reactive today, loose and lacking in slab structure. Earlier this week observers reported finding surface hoar on Delancey Ridge and the Hairpin Valley in the typical valley to mid-slope locations.  They also noted steeper S-SW slopes had a thin sun crust.  It remains to be seen if this layer warrants more attention over the coming days and weeks with incremental loading events.  Enjoy the more moderate temperatures tomorrow and Friday because we're headed for an arctic blast (or something like it) over the holiday weekend.  

A 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 3-5 feet below the surface, especially on slopes above 6,000ft.  While avalanches have been confirmed on this layer, observers continue to find varied test results on the crust including some that indicate the potential for triggered avalanches. 

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