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Avalanche Forecast

Archived

Dec 19th, 2017–Dec 20th, 2017

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

Regions

Olympics.

The avalanche danger will be decreasing on Wednesday. But the rate of this decrease is less certain so you will need assess conditions and be able to make wise terrain choices if you are out on Wednesday.

Detailed Forecast

Light snow showers should end Tuesday night with mostly sunny weather at Hurricane on Wednesday. Expect decreasing or lighter NW-NNW alpine winds and much cooler temperatures.

This means the avalanche danger will be decreasing on Wednesday. But the rate of this decrease is less certain so you will need assess conditions if you are out on Wednesday.

Storm slab will linger on Wednesday in areas that had at least several hours of rapidly accumulating snowfall and that developed weak storm layers on Tuesday.

Given the winds, small to large wind slabs are still likely near and above treeline, mainly on NW through SE aspects near ridges, but are possible on other aspects. Avoid ridges or terrain features with firmer wind transported snow.

Loose wet avalanches will not be listed as an additional problem due to the low sun and cool temperatures. But start to watch for loose wet conditions on steep solar slopes if you see significant rollerballs or find surface wet snow deeper than a few inches.

Remember that beneath snow received during this storm cycle, early season terrain hazards exist, especially at lower elevations. Expect terrain hazards with poorly covered rocks, vegetation and creeks, particularly on south-facing terrain, at lower elevations, and on exposed ridges where wind events have stripped much of the season's snowcover.

Snowpack Discussion

Fair weather dominated over the Olympics most of the first half of December. This allowed snow to consolidate and created varied snow surfaces including surface hoar and near surface faceted snow.

West flow began to carry a series of fronts across the Northwest starting about December 16th. But light rain at Hurricane Ridge should have destroyed surface hoar or near surface faceted snow that may have persisted on northerly aspects. 

The last front in the series is crossing the Northwest on Tuesday. Storm snowfall totals Wednesday morning at Hurricane will be in the 2-3 foot foot range. South to southeast winds in the teens with gusts to the 20-30 mph range have been seen Tuesday. Temperatures rose a bit to about 31 at Hurricane Tuesday and began cooling by Tuesday afternoon.

Observations

No recent observations.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.