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Avalanche Forecast

Archived

Feb 9th, 2017–Feb 10th, 2017

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

Regions

Olympics.

After a period of wild weather Wednesday night and Thursday that closed major highways and limited observations, there is a higher than normal amount of uncertainty about the snowpack heading into Friday. Account for the uncertainty with more conservative travel plans than you might otherwise given the same danger rating.

Detailed Forecast

What a difference a day makes as we quickly transition from mild and wet to cool and showery weather on Friday. Snow levels will slowly lower Thursday night and lower further during the day on Friday. Showers should decrease overnight but then increase again late Friday morning as a low pressure system passes to our north. SW winds will be moderate to occasionally strong Thursday night and Friday at Hurricane Ridge. 

After a period of wild weather Wednesday night and Thursday that closed major highways (in the Cascades) and limited observations, there is a higher than normal amount of uncertainty about the snowpack heading into Friday. Account for the uncertainty by choosing more conservative travel plans than you might otherwise given the same danger rating.

Moderate to occasionally strong SW winds will transport new and recent snow onto lee slopes near and above treeline. Wind slab may build down into the below treeline band on Friday. NW-SE aspects will be identified in the elevation/aspect diagram but watch for firmer wind transported snow on a variety of aspects.   

Despite the cooling trend, new storm slab instabilities may develop during periods of intense showers.   

For areas west of the Cascade crest including the Olympics, wet slabs will be listed as unlikely due to the cooling trend. However, avoid travel below unsupported slopes, especially near and below treeline, with the low likelihood/high consequence of large wet slab avalanches in mind. Wet slab releases are hard to predict and can happen a day or two after peak warming and rainfall.   

Snowpack Discussion

Weather and Snowpack

A strong storm cycle was seen Friday through Monday with about 3 feet of snow accumulating at Hurricane Ridge. 

A strong plume of moisture brought heavy rain to the west slopes of the Cascades and Olympics. About 2 inches of water fell mainly as rain at Hurricane Ridge from Wednesday afternoon through Thursday afternoon with significant snowpack settlement. A strong cold front swept through mid-day. Bands of light to moderate showers in SW flow followed the front with a slow cooling trend beginning Thursday afternoon.  

Recent Observations

No observations have been received since last Saturday. 

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.

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.