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Avalanche Forecast

Archived

Jan 17th, 2017–Jan 18th, 2017

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

Regions

Olympics.

A drastic change from the recent weather is underway. Very wet and mild weather should substantially increase the avalanche danger through Wednesday. Natural wet snow avalanches are likely and travel in avalanche terrain is not recommended.  

Detailed Forecast

An avalanche warning is in effect through Wednesday afternoon: Expect periods of heavy rain and strong winds to continue Tuesday night through Wednesday afternoon. The wet and milder weather should substantially increase the avalanche danger through Wednesday.

The heavy precipitation with a warming trend through Tuesday night and Wednesday will impact the Olympics including the Hurricane Ridge area. A natural avalanche cycle should occur with the heaviest precipitation.

An abundance of weak and cold snow in the upper snowpack especially near and below treeline combined with the potential for rapid warming and high precipitation rates would lead to very dangerous avalanche conditions during this period and backcountry travel is not recommended. 

The 12/17 PWL which has been largely unreactive as of late may awaken during the expected upcoming warm and wet period with the potential to produce large and destructive avalanches down to this layer. 

Snowpack Discussion

Weather and Snowpack

The last significant snowfall in the Hurricane Ridge area occurred over a week ago, with 6 inches of new snow reported by NPS staff Monday 1/9. 

An upper ridge over the northeast Pacific Ocean has caused fair weather Thursday through Monday over the Olympics and Cascades with mostly light winds and moderating temperatures west of the crest and at higher elevations. Hurricane Ridge topped out at 40 degrees on Saturday and Sunday and 39 Monday 1/16. 

Surface hoar and near surface faceting has been noted in the Olympics and Cascades in sun and wind sheltered locations below treeline. Sun crusts have formed on steeper solar aspects over the last few days. 

Warm, wet and windy weather has returned to the Olympics as of Monday night with the rain really increasing Tuesday afternoon, 1/17 to all elevation bands.

Recent Observations

NWAC pro-observer, Matt Schonwald was in the field with NPS rangers in the Hurricane Ridge area Friday, 1/6. Matt traveled to Steeple Rock on the Obstruction Peak Road. The persistent weak layer from 12/17 was evident in the two distinct areas where snow tests were performed. The layer ranged in depth from 110 cm on SSW aspect to 135 cm on NW aspect. While reactive in deep snowpack tests and PST's, stiff overlying layers and the fact the layer is deeper than 1 meter make human triggering of this layer unlikely. 

NWAC pro-observer, Matt Schonwald was out on Klahane Ridge on Friday, 1/13 and on a south slope at 5170 feet found about 90 cm of snow with no reactive layers over the 12/17 PWL. The PWL gave a PST60/100 End result, so we still need to watch this layer.

 

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.