Avalanche forecast

Stevens Pass

Dec 19 – 20, 2019Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

Expect very dangerous avalanche conditions on Thursday night and Friday. Heavy snowfall, strong winds, and a rapid rise in temperatures will combine to create unstable snow and natural avalanches. Stay off of, and out from underneath places where avalanches can start, run, and stop. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Heavy snowfall rates, strong winds, and warming temperatures will create thick storm slabs. The temperatures for the initial round of snow were cool, and the snow that fell was lower density. With the arrival of warm air and strong winds, we can expect heavy, cohesive and wet snow to overload either this weaker layer, or the new and old interface. Signs of instability for storm slabs are shooting cracks, audible whumphing, and recent slab avalanches. Stay off of, and out from underneath steep slopes. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Rain on snow will weaken the upper snowpack, causing wet avalanches. Look for roller balls, wet debris piles or other fan shaped avalanches as key signs to this type of instability. Wet slab avalanches are not out of the question either. In any case, heavy, water soaked snow will create dangerous avalanche conditions and travel will be challenging. Avoid steep slopes with rain soaked snow.

Snowpack Discussion

December 19th, 2019 (The regional synopsis is updated every Thursday @ 6 pm)

Let’s take a moment to recap what happened over the past week:

A potent winter storm arrived on the 12th, adding to the very shallow snowpack throughout the region. Anywhere from 6-36” of snow fell between the 11th and 15th. Places like Mt Baker, Paradise, Mt Hood, and White Pass were the winners regarding snowfall, with quite a bit less for areas further east of the crest like Mission Ridge, Blewett Pass, and Washington Pass. 

The most notable avalanche activity occurred in the Mt. Baker backcountry where numerous human triggered storm slab avalanches occurred (with several big enough to injure, bury, or kill a person). The majority of these occurred on upper elevation, north and east facing terrain. Besides the danger posed by the size of the avalanche, many slides quickly revealed rocks and other obstacles barely hidden below the snow surface. 

The storm layer took time bond with the underlying snow surface, and we saw the likelihood of triggering slab avalanches slowly decrease over a handful of days. The avalanche danger was at Considerable for many places on Saturday the 14th, then tapered to Moderate on Sunday, and eventually reached Low in many places by Tuesday and Wednesday. 

A large, human triggered avalanche on the old snow interface. East aspect of Table Mountain (West-North Zone) at 5,500ft. December 15,2019. Photo by Brooks Broom. 

Backcountry travelers have noted generally thin and shallow snowpacks, with a range of structures across the region. Many folks were skeptical of the layering they found. People were able to dig down and observe weak layers in many areas. These were buried in late November and early December. In some places they presented as weak snow over a crust, in others, a layer of feather-like surface hoar. Cold temperatures have likely preserved many of these layers, and will be worth considering as the snow piles up.

Below is a list of commonly visited locations and their snowpack depths in inches (as of December 19th at 4am). Check the weather station hourly data feed and watch as the subtropical javelin of moisture (also known as a strong atmospheric river) changes conditions dramatically over the next few days. 

Total Snow Depth in Inches as of December 19th at 04:00 AM.

-Matt Primomo

Regions covered