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Avalanche Forecast

Archived

Apr 3rd, 2018–Apr 4th, 2018

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.

Stormy weather with rising snow levels will increase the avalanche danger Wednesday creating dangerous avalanche conditions at all elevations. Avoid all open slopes greater than 35 degrees Wednesday as new avalanche problems grow and develop. Wet heavy snow and wind will build new and reactive wind and storm slabs. At lower elevations receiving rain, expect wet avalanche conditions to develop.

Detailed Forecast

Dangerous avalanche conditions will develop Wednesday. A storm will bring renewed rain and snow, strong winds and rising freezing levels to the Mt Hood area. 

You will be able to trigger Wind Slabs on steep slopes near or below ridgelines at higher elevations. Watch for clues like variable snow height, drifts, cornices, and stiff snow that produces cracking. These are all indicators that you could trigger a Wind Slab. You can avoid triggering these avalanches by steering around steep roll-overs, unsupported features, and obvious start zones where you suspect Wind Slabs.

New snowfall amounts and wind speeds will increase with elevation, and this will increase the potential for larger avalanches at higher elevations.  

Snow changing to rain below treeline will make Loose-Wet avalanches likely at lower elevations. Expect potentially large Loose-Wet avalanches to occur as wet heavy snow or rain quickly destabilizes recent snow. 

Cautious route-finding and conservative decision-making will be essential Wednesday as triggered avalanches will be likely Wednesday in steep wind loaded terrain at higher elevations and all steep terrain below treeline.

Snowpack Discussion

In general 12-14 in. (30-35 cm) of new snow fell in the Mt Hood area Sunday and Monday. Strong westerly winds during the storm and through the day Tuesday redistributed much of the recent snow at higher elevations, forming wind slabs on lee slopes. The new snow fell on a firm melt-freeze crust in many locations forming an initially poor bond. Wind slabs were less reactive to human triggers Tuesday, but still producing 1-3 ft avalanches with explosive control above treeline, mainly on N-E facing slopes.  

The recent 1 ft plus of snow has settled and stabilized below treeline as of Tuesday where there were no reported avalanches. 

There are currently no significant layers of concern in the mid or lower snowpack.

Observations

Tuesday, Mt Hood Meadows pro patrol reported Wind Slabs releasing with explosives on N-E lee slopes above treeline, averaging 1 ft. Wind Slabs were no longer sensitive to ski trigger. Below treeline, storm layers had settled and stabilized with no avalanches reported near or below treeline. 

On Monday, Mt Hood Meadows ski patrol reported 1-2 ft (30-60cm) Wind Slab avalanches on lee slopes above treeline during control work. Near treeline, 6-12 inch (15-30cm) Wind Slabs were triggered on wind loaded slopes. Below treeline the 12-14 inches (30-35cm) of recent storm snow lacked slab properties, however Dry Loose avalanches were possible.

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 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.