Avalanche Forecast

Archived

Jan 4th, 2015–Jan 5th, 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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Dangerous avalanche conditions are expected Sunday night and early Monday. The avalanche danger should lower during the day as rainfall comes to an end.

Detailed Forecast

Moderate to heavy rain should reach up into the above treeline elevation band through Monday morning. Luckily, the rainfall should quickly ease Monday morning although the high snow levels will stick around.

This will orient the avalanche type toward wet slab and wet loose on Monday. Rain should quickly load snowfall received earlier in the storm and result in widespread natural loose wet avalanches especially in steeper terrain. Natural wet slabs, mainly on lee aspects near and above treeline, have the potential to be larger and more destructive. Due to low snow cover, the avalanche danger will quickly decrease in the below treeline band at lower elevations.

Snowpack Discussion

On Sunday, light snow along with moderate westerly transport winds accumulated new snow onto lee aspects with rising temperatures leading to inverted new snow layering. Pro-observer C.J. Svela did not find the new snow particularly reactive in White River Canyon around mid-day, but the heaviest warming and precipitation had not occurred yet. Precipitation intensity should increase rapidly Sunday night with quickly rising snow levels. Rain should reach well into the above treeline elevation band by early Monday morning. Avalanche concerns for Mt. Hood will be directly related to the incoming storm.

A generally strong mid and lower snowpack is expected at Mt Hood.

Problems

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.

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.