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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 possible, human triggered probable.

Regions

Mt Hood.

Another round of storm slab and wind slab are likely Wednesday, with new wind slab mainly forming on lee slopes ranging from N-SE facing, especially by afternoon as wind speeds increase. Loose dry avalanches in non-wind affected terrain will be difficult to manage on steeper slopes, so use extra caution around terrain traps. 

Detailed Forecast

Another Pacific frontal system, in the long series of recent storms, is moving into the Mt Hood area Tuesday evening. This next system will cause renewed light to moderate snow and light to moderate westerly winds Tuesday night. This should begin to build new areas of wind slab on lee slopes below ridges and create some isolated storm slabs. Moderate to heavy showers should persist with increasing westerly ridgetop winds through the day Wednesday. 

Dangerous avalanche conditions should persist Wednesday in all elevations bands and especially in the near and above treeline zones. 

Expected avalanches should remain within the near surface storm related weak layers. Watch for evidence of wind deposited snow or pillows. Test for inverted of 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 steeper 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, two to over three feet in places! There was a snow immersion fatality in a tree well in bounds at Snoqualmie on Saturday, and a close call at Crystal Mtn Tuesday, so always travel with a partner. 

Snowpack Discussion

About 4 feet of new snow has fallen in the Mt Hood area over the past five days! Including 10-15 inches of new snow deposited from a strong storm Monday! ?The most recent reports Tuesday from patrol at Mt Hood Meadows indicate avalanches are mainly confined to recent storm and wind slab layers mostly 6-12".

A stiffer wind slab layer was found sandwiched between two weaker snow layers at about 6600 feet Tuesday.   

The crust formed December 17th is now buried deeply and may have broken down or just not be involved in recent avalanches and is becoming less a player with each day's new storm snow accumulations. 

 

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.

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.