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Archived

Avalanche Forecast

Apr 7th, 2015–Apr 8th, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Mt Hood.

Recent snowfall followed by likely increasing sunshine Wednesday could make for increasing avalanche danger on Mt. Hood, so be aware of quickly changing surface snow instability.   

Detailed Forecast

Showers should end by Wednesday with clearing skies, light winds and relatively cool temperatures. Recent new snow may have mostly settled and stabilized over the past few days, but in some areas, watch for greater new snow or wind deposited slabs, especially near and above treeline where there may be slightly more recent snow. Avalanche problems Wednesday will revolve around recent storm snow.  

It's April, so be aware of the increased solar input reaching more aspects and affecting the snow surface quickly. Loose wet avalanches involving shallow amounts of recent storm snow will be possible Wednesday, especially during direct sunshine and during afternoon warming.    

While most storm slabs should have settled by Wednesday, continue to watch for evidence, such as new snow bonding poorly to aspects with surface crusts or fail on storm snow instabilities formed during periods of showers. 

Due to the continued cool weather, cornices won't be listed as an avalanche problem either, but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.

Snowpack Discussion

Periods of active weather and mountain snowfall have finally graced the PNW since about mid March onward. 

A front moved across the Northwest Tuesday, followed by showers and rapid cooling Tuesday night and Wednesday. Storm snow from this system was about 9-15 inches at Mt Hood. The patrol at Meadows on Wednesday reported that the storm snow was surprisingly less reactive than anticipated with few explosive and no ski triggered avalanches observed. 

1-3 inches of new snow were recorded at NWAC stations on Mt. Hood Friday night, with some moderate westerly wind transport above treeline, but only very isolated pockets of wind slab up to 1 ft were found above treeline on lee aspects. 

Showers deposited an additional 6-10 inches of new snow as of Monday morning, April 6th and a trace to 2 inches more as of Tuesday. Some local wind transport was noted by patrol at Hood Meadows Monday morning and subsequently some very soft slab conditions noted. 

Snowpack problems at Mt Hood should remain in the upper or surface layers. The mid and lower snowpack at Mt Hood consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this season. Many areas at low elevations do not have enough snow to cause an avalanche danger.

Avalanche Problems

Loose Wet

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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Aspects: East, South East, South, South West, West.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1

Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1