Avalanche Forecast

Archived

Feb 11th, 2016–Feb 12th, 2016

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Rainfall will renew the loose wet avalanche potential on all aspects of steeper slopes. New snowfall should bond well to a moist snow surface in most locations, but wind-driven snow may build unstable wind slab on lee aspects of higher terrain by Friday afternoon.

Detailed Forecast

Mild snow levels should keep precipitation in liquid form until a cold front passes through the Cascades Friday mid-afternoon with snow levels lowering to 5000 feet by late afternoon in the Mt. Hood area. Precipitation should be light in the morning and light to moderate in the afternoon.

Rainfall will renew the loose wet potential on all aspects of steeper slopes. New snowfall should bond well to a moist snow surface in most locations, but wind-driven snow may build unstable wind slab on lee aspects of higher terrain of Mt. Hood by late Friday afternoon.

Continue to watch for loose wet avalanche potential above terrain traps such as above cliffs, near gullies or where avalanche debris would deeply accumulate. These are the types of places that even small wet avalanches can have serious unintended consequences.

Avoid cornices along ridges and slopes below cornices since cornices may still be weaker due to the warm weather.

Snowpack Discussion

Weather and Snowpack

A large upper ridge and warm air mass aloft over the West Coast from this past Sunday through Wednesday led to the warmest weather of the winter. During this stretch temperatures were generally well above freezing. Freezing levels came down a few notches Thursday, but mild conditions continued with spotty light rain increasing Thursday afternoon in the Mt. Hood area.

The very warm temperatures and solar effects caused loose wet avalanches, snowpack consolidation, and melt-freeze surface crusts. This will have further stabilized the lower and mid snow pack and turned the most recent storm snow into moist to wet snow in most areas.

Recent Observations

Limited loose wet snow conditions were seen by Tuesday at Mt Hood by the pro-patrol. Moderate winds limited surface snow melt near and above treeline. More significant wet snow conditions were seen below treeline Tuesday with limited loose wet avalanche activity.

Small loose wet avalanches were reported as easy to initiate below 4600 feet Wednesday by Meadows pro-patrol, with similar conditions likely Thursday below treeline.

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.

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.