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Avalanche Forecast

Archived

Dec 13th, 2018–Dec 14th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Strong storms earlier this week have formed unstable wind slabs. These conditions are beginning to improve, however, continue to watch for recently wind-drifted or actively wind-loading slopes, primarily near and above treeline. 

Snowpack Discussion

Regional Synopsis 20181213

Winter is here.

A productive winter storm pattern has elevated the avalanche danger and provided an interesting start to the season.  

A quick breakdown:

  • Tuesday and Wednesday saw a significant localized avalanche cycles.

  • We have a lot of new snow...2’ to 5’ above 4500ft.

  • We’ve gotten a lot of wind.

  • We have weak layers near the ground.

Dangerous avalanche conditions will persist over the next couple of days. That said, it is early season and the flavor of avalanche you may run into is likely a function of elevation, timing, and dumb luck.

Here are some basic emerging patterns:

  • Snowfall totals so far this week (Monday morning to Thursday evening) illustrate more recent snowfall in the north than the south:

    • Mt. Baker: 55”

    • Washington Pass: 29”

    • Stevens Pass: 37”

    • Snoqualmie Pass: 28”

    • Paradise: 38”

    • Mt. Hood Meadows: 13”

  • Upper versus Lower Elevations: The change in the snowpack is still pretty dramatic with elevation. Height of snow decreases rapidly below 4500’ at Baker and Washington Pass, 5500’ at Crystal/Rainier. The Passes have better low elevation coverage, but it's still pretty thin below 4000’. With additional warm storms in the forecast, this pattern is expected to continue for awhile.

  • East versus West: Loading along the East slope has been more incremental, and a  variety of buried facet and surface hoar layers may be found. This is most pronounced near WA Pass. Although significant snowfalls and precip totals have resulted in thicker, more homogeneous snowpack in the western zones, lingering weak layers near the ground will persist through the week.

The uncertainty of how reactive our buried weak layers are will carry into the weekend. Be cautious and get home safe.

 

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.