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Archived

Avalanche Forecast

Jan 14th, 2017–Jan 15th, 2017
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Mt Hood.

Little change in the avalanche danger is expected Sunday with recent wind slabs primarily found on N-SE aspects. However be alert for wind slab on all terrain aspects due to shifting winds and cross-loading during the last storm.

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. Alpine winds will begin to increase on Sunday out of the North. 

Recent wind slabs at Mt Hood should be primarily on N-E aspects but be alert on all terrain aspects for firmer wind transported snow near and above treeline. 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. 

Snowpack Discussion

Weather and Snowpack

A low pressure system tracked across Oregon Tuesday morning through Wednesday afternoon. Mt. Hood was stacking up the new snow Tuesday with 15-20 inches falling Monday night through Wednesday mid-day. Winds were generally light to moderate in this storm, but E winds increased mid-mountain Tuesday afternoon, then switched to SW Wednesday.

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. 

Surface hoar and near surface faceting has been noted widely throughout the Cascade range 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

On Wednesday, Meadows pro-patrol did not venture above about 6600 feet due to white-out conditions. Below this elevation, in the mostly below tree line band, sheltered slopes were maintaining right side up powder conditions that lacked any slab structure, providing excellent conditions.

On Thursday, the pro-patrol reported one natural 8 inch x 300 foot wide natural slab avalanche that occurred Wednesday on a south slope at 6500 ft. Otherwise on Thursday only pockets of 4-10 inch wind slab were released by explosives on N-NE slopes in the near and above treeline due to SW winds on Wednesday.

A couple reports for Mt Hood area available via the NWAC Observations page for Thursday. A skier on the north side of Mt Hood noted E and W wind effects and potential wind slab in the near and above treeline. Another skier on Pea Gravel Ridge noted limited, thin wind slab near the top of the Ridge but otherwise snow was right side up and cornice and ski tests gave no results.

NWAC pro-observer Laura Green was touring in the east fork of Hood River up to 6100 ft on Friday. She found the upper snowpack generally non-reactive in snowpack tests with good skiing conditions especially below treeline. Good surface hoar growth was noted up to 6100 ft. 

Avalanche Problems

Wind Slabs

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.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1