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Avalanche Forecast

Archived

Jan 31st, 2018–Feb 1st, 2018

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

Regions

Mt Hood.

Stubborn wind slabs may still be triggered in specific areas Thursday near and above treeline. Use caution near steep wind loaded open slopes. A rising snowline through the day will allow for generally small loose wet avalanches in steep terrain below 6000 feet. Be aware of your exposure to terrain traps on steeper slopes as the likelihood of triggering a loose wet avalanche increases during the afternoon. 

Detailed Forecast

Scattered light snow showers in the morning should become light rain and snow by the late afternoon and early evening. Snow levels will gradually climb through the daylight hours and again further overnight as precipitation and winds increase markedly. 

Stubborn wind slabs may still be triggered in specific areas Thursday near and above treeline.  Use caution near steep wind loaded open slopes. Cornices are likely large and should be given a wide berth as they often break back further than you expect. 

A rising snowline through the day will allow for generally small loose wet avalanches in steep terrain below 6000 feet.  Be aware of your exposure to terrain traps on steeper slopes as the likelihood of triggering a loose wet avalanche increases during the afternoon. 

Snowpack Discussion

Up to 12 inches of snowfall along with a cooling trend Tuesday and Wednesday followed a brief period of heavy rain on Monday. Moderate Westerly winds finally began to ease on Wednesday. The most recent crust was firm near and above treeline and semi-breakable below treeline on Wednesday.  

A significant warm up January 28-29th followed on the heels of a long and stormy period which built deep wind slabs near and above treeline. During this break in the weather, explosives were able to trigger multiple very large avalanches. The avalanches entrained wet snow at lower elevations to become very large and powerful, and even in one case knocked down timber.

Observations

On Wednesday, Mt Hood Meadows Pro Patrol triggered wind slabs of 2-6" with up to 12" pockets on some NE slopes above treeline. Above 5800' including the near and above treeline elevation bands, the surface snow was sculpted by recent winds with widespread sastrugi and scoured ridgelines. Below this elevations, 6-8" of snow was well bonded to the 1/29 semi-supportable crust.  

Mt Hood Meadows Pro Patrol Tuesday reported widespread large and hard wind slabs reactive on north through east aspects, near and above treeline with some small loose dry and storm slab possible to trigger below treeline. A rain crust was present up to 6600 ft.

Mt Hood Meadows Pro Patrol Sunday reported multiple very large artillery-released avalanches with crowns up to 12 ft range, running on steep NE and ENE terrain above treeline and travelling very long distances, in one case snapping 20+ year old trees. Snow pits in the 5000 and 7000 ft range identified 1 mm rounding, wet facets on top of a 1/18 freezing rain crust as the likely weak-layer/bed surface for these very large slides. Given the large amount of recent wind transport, the depth of this layer varied widely.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.