Avalanche Forecast

Archived

Mar 8th, 2018–Mar 9th, 2018

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

The avalanche danger will increase during the day on Thursday with very windy conditions quickly forming fresh Wind Slabs. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. Rainfall will increase the likelihood for Loose Wet avalanches below treeline. The avalanche danger will increase further Thursday night.

Detailed Forecast

The avalanche danger will increase during the day on Thursday as a storm system brings light to moderate rain and snow to Mt. Hood along with very windy conditions. Look for developing Wind Slabs on lee slopes near and above treeline that you can easily trigger. Watch for cracking, wind stiffened snow, and freshly formed drifts. Steer around fresh wind features, convex rolls, and slopes holding a foot or more of new, cohesive snow that are 35 degrees and steeper. Shallow Storm Slabs may develop by the afternoon in wind sheltered terrain. The avalanche danger will continue to increase Thursday night.

The rain/snow line is forecast to rise to 5000-5500' Thursday. Rainfall will raise the likelihood of small Loose Wet avalanches on steep slopes below treeline, especially those that have received fresh snowfall. Avoid steep slopes below treeline connected to terrain traps, where even a small Loose Wet avalanche could have unintended consequences.

Snowpack Discussion

Temperatures were above freezing at NWAC stations at Mt. Hood Wednesday. Combined with overcast skies, this likely moistened the snow surface on all aspects near and below treeline. Loose Wet avalanches were reported Tuesday on sunny aspects.

Mt. Hood received 3" of new snow Sunday night through Monday morning and west winds were transporting snow onto lee slopes (mostly easterly aspects) forming shallow wind slabs about 8" deep.

In many locations more than 3’ of snow now sits on a firm buried crust layer (2/17). This crust has been reported up to 6600’ by professionals in the region. There are currently no significant layers of concern below the 2/17 crust.

Observations

NWAC pro-observer Laura Green was in Mitchell Creek Monday and observed active wind loading occurring near and above treeline. No new or recent avalanches were observed.

On Monday, Mt. Hood Meadows Pro Patrol reported west winds transporting snow, 8" of new and generally non-reactive wind slab on lee aspects limited to E facing slopes. Winds eased mid-day. Small loose wet avalanches occurred on solar, especially below treeline.

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.

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.