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Avalanche Forecast

Archived

Dec 23rd, 2015–Dec 24th, 2015

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

Storm slab, wind slab, cornices and deep unconsolidated snow are all key features to plan to avoid on Thursday.

Detailed Forecast

A cool upper trough will continue to sink south over the Pacific Northwest on Thursday. West winds should begin to decrease Thursday initially in the Olympics and north Cascades. Snow showers Thursday along the west slopes should bring another 5-10 inches to the central and south including Mt Hood.

Dangerous avalanche conditions should persist Thursday with more new or recent storm and wind slab should likely. Natural or triggered storm and wind slab avalanches should remain within recent storm layers but could move fast. Watch for evidence of wind deposited snow or pillows. Test for inverted strong over weak storm snow and give cornices a wide margin.

Loose dry avalanches in non-wind affected terrain will be difficult to manage on steep slopes. Even a small loose dry avalanche could have unintended consequences such as knocking you off your feet and into a terrain trap.

The recent unconsolidated storm snow is now very deep in many places!. There was a snow immersion fatality in a tree well in bounds at Snoqualmie on Saturday so always travel with a partner.

Snowpack Discussion

The Christmas snow globe keeps giving here in the Pacific Northwest! It's gotten very deep out there including at Mt Hood. By Thursday morning NWAC sites at Mt Hood will have received about 6-7 FEET of snow in less than a week.

NWAC pro observer Laura Green was fortunately touring Wednesday in remote parts of the Mt Hood Meadows ski area and reported widespread, sensitive storm slab of 1-2 feet on north to east slopes in the 4500-6000 range.

 

 

Problems

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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.