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Avalanche Forecast

Archived

Jan 16th, 2015–Jan 17th, 2015

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

Watch for warming and rain affecting recent storm snow, mainly where local deposits are greatest, such as lee slopes below ridges at higher elevations. Avoid travelling on terrain connected to larger open slopes above as some slides starting at higher elevations may run far and fast on underlying crust surfaces. 

Detailed Forecast

A strong warm front should spread increasing precipitation to the Cascades, spreading from south to north early Saturday with strong winds and substantial warming and freezing levels climbing above 8,000 feet. 

The rain should cause an increasing danger, mainly near and above treeline, in those areas where deeper recent storm snow exists. Where slabs have formed warming and rain should make wet slab releases possible, while the problem at lower elevations should be confined to loose-wet avalanches.

It should be a good day to let the rain have its way and wait for the cooling and new snow to follow. 

On backcountry travel safety note, watch for terrain hazards (exposed rocks, trees, streams, etc.) at lower elevations and on wind scoured aspects.

 

Snowpack Discussion

A fast moving front late Thursday, followed by showers Friday has deposited about 6-12 inches of storm snow as of late Friday afternoon. While early Friday morning observations at 6600 ft at Mt Hood Meadows, indicated a weak bond of new storm snow to the old crust, subsequent observations in the afternoon indicated there were very few avalanche releases with explosive control. Shallow storm snow, rough underlying crust surfaces and non-uniformed loading are some contributing factors for that.

Under the recent storm snow, the snowpack in most areas consists of very strong surface melt-freeze crusts of varying thicknesses formed over stabilized rounded grain layers. Surface crusts have been recently reported to be fairly rough, which may decrease the ease of triggering new slabs.  

The overall snowpack remains well below normal for this time of year, and some windward or southerly aspects have little if any snow cover.  With the overall strength of the snowpack, any newly developing storm slab avalanches should be limited to new snow. 

Problems

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.