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Avalanche Forecast

Archived

Jan 20th, 2018–Jan 21st, 2018

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

Regions

Mt Hood.

Avalanche conditions will worsen throughout the day on Sunday. Winds throughout the storm period have reshaped surface snow creating a variety of snow surfaces including firm wind slabs. Travel with large safety margins Sunday, as wind slabs can be very difficult to assess.

Detailed Forecast

A frontal system will slowly move into the Mt. Hood area on Sunday with increasing precipitation and winds expected during the daylight hours. Wind and storm slabs developed over the past couple of days will continue to grow and potentially become more reactive. Expect avalanche conditions to worsen throughout the day.

Above treeline a lack of recent information has created a high degree of uncertainty. Expect very difficult travel conditions due to poor visibility and varied snow surface conditions.

Below treeline smaller amounts of new snow continue to limit avalanche danger. Pay attention to exposed features where winds may alter snow surface conditions, creating wind slabs normally found at higher elevations.

Snowpack Discussion

New storm snow continues to accumulate in the Mount Hood area. By Saturday afternoon, 8-12 inches of storm snow has fallen since Wednesday, with more snow expected at higher elevations. The bond between the new snow and 1/17 crust is gaining strength. 

Moderate to strong westerly winds throughout the storm period has significantly redistributed recent storm snow. Reports indicate some windward slopes have been stripped down to the old surface crust. On lee slopes wind deposited snow drifts can exceed 2 feet.

Very poor visibility and dangerous travel conditions has made observations in above treeline terrain unobtainable. A high degree of uncertainty exists above treeline.

Observations

On Saturday Mt Hood Meadows Patrol reported 5 inches of snow in the past 24hrs. Near treeline, westerly winds created stubborn wind slabs on lee aspects. 

NWAC Pro Observer Laura Green was in the near treeline area of Heather Canyon Friday. Recent storm snow had been highly re-distributed by strong winds. Sensitive wind slabs were found on exposed slopes. Mostly shallow storm snow was found well bonded and not reactive to tests below treeline.

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.