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Avalanche Forecast

Archived

Jan 14th, 2017–Jan 15th, 2017

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

Regions

Olympics.

Little change in the avalanche danger is expected Sunday with recent wind slabs primarily found on N-W-S aspects. However be alert for wind slab on all terrain aspects due to local loading patterns. 

Detailed Forecast

The upper ridge will linger over the northeast Pacific Ocean through the weekend. High clouds should pass through the region Saturday night but mostly sunny skies are expected on Sunday. Temperatures should continue to moderate Sunday.

Recent wind slabs should be found primarily on N-W-S aspects. The benign weather will continue to slowly allow these layers to stabilize. Remember that firmer wind transported snow is always your best sign of wind slab layers.

Small loose dry avalanches are possible in steep wind sheltered terrain but will not be listed as an avalanche problem.  Small loose wet avalanches will also be possible on steeper solar aspects Sunday. 

Continue to identify the 12/17 buried PWL in snowpits and avoid areas where the overlying snowpack is shallower such that affecting this layer would be more likely.

Snowpack Discussion

Weather and Snowpack

A pair of warm fronts moved across the Northwest last weekend causing see-sawing temperatures to near or above freezing for areas away from the Passes including Hurricane Ridge. 6 inches of new snow were reported by NPS staff Monday 1/9 at Hurricane Ridge. 

Although the precipitation gage didn't record any tips, NPS web cameras showed steady light snowfall at Hurricane Ridge all day Tuesday with light upslope snow showers. Light N or NE winds were increasing in the afternoon.

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

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. The best riding and skiing conditions have generally been reported in less wind and sun affected areas below treeline during this stretch of fair weather.

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

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.

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.