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Avalanche Forecast

Archived

Dec 30th, 2017–Dec 31st, 2017

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

Regions

Mt Hood.

Look for signs of recently wind transported snow such as snow drifts, fresh cornices, and uneven snow surfaces. Identify and avoid stiff wind loaded snow on lee and cross loaded slopes.

Detailed Forecast

Clearing skies, warming temperatures, and decreasing winds Sunday should allow the snowpack time to gain strength.

Wind slabs will continue to be a problem into Sunday especially at higher elevations. Look for signs of recently wind transported snow. Identify and avoid wind loaded terrain below ridgelines and cross loaded terrain features. While we expect wind slabs to primarily exist above treeline, keep a watchful eye out for exposed terrain features near treeline where wind slabs may have formed.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

Snowpack Discussion

Saturday afternoon brought to an end a very active and wet weather pattern at Mt Hood.

Moderate to strong winds have continued to redistribute new snow at higher elevations forming wind slabs on ridgeline and cross loaded features. Variable snow surface conditions exist including wind stripped snow and firm wind slabs.

At lower elevations recent rain has created firm melt freeze crust capped with a few inches of snow.

A variety of rain and freezing rain crust exist in the upper snowpack depending on elevation. Current observations do not suggest these layers to be reactive.

Observations

Saturday a report of a large natural avalanche in Clark Canyon was received. Visibility limited the extent of the observation.

On Friday, NWAC Pro Observer Laura Green was in Sand and Heather Canyons. In terrain from 4850-6600 feet elevation, she found moderate to hard tests with progressive collapse at crusts at crusts down 5 and 10 inches. She noted that the Hood snowpack absorbed the water "like a thirsty sponge." 

On Friday morning, Mt. Hood Meadows pro patrol reported the freezing rain crust to have been melted by the rainfall at 5200 feet, where where boot penetration was 18”. The upper snowpack was moist, not wet. Standing water was observed at 6500 feet with no avalanches. 

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.