Avalanche Forecast

Archived

Feb 22nd, 2018–Feb 23rd, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

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 possible, human triggered probable.

Regions

Mt Hood.

New shallow wind slabs will build during the day on Friday above treeline. You will most likely be able to trigger these avalanches on steep slopes near wind drifting and blowing snow, and below fresh cornices. In sheltered areas, loose snow conditions will continue. Avoid steep slopes where even small loose dry avalanches can have larger consequences such as above cliffs, creeks, and gullies.

Detailed Forecast

New shallow wind slabs will form Friday, especially above treeline, as the next round of precipitation and wind begins to impact Mt Hood in the afternoon. The avalanche danger will rise slightly throughout the day as slabs grow deeper and become easier to trigger. Look for areas of wind blowing snow, plumes, fresh cornices, and drifting snow. Avoid steep slopes where wind deposition is occurring.

In sheltered areas, loose surface snow will exist. You will be most likely to trigger loose snow avalanches on slopes greater than 35 degrees. Avoid slopes with higher consequences such as above cliffs, gullies, and creeks where even small avalanches can harm you.

Any avalanche occurring Friday will have the potential to entrain loose surface snow and grow large.

Snowpack Discussion

Several natural loose dry avalanches were reported Wednesday on slopes steeper than 35 degrees. These avalanches resulted from snow falling with generally cold temperatures and light winds creating loose snow surface conditions at all elevations. The Mt Hood area has received several feet of light dry loose snow over the last several days. Little to no slab formation has been reported in the recent snow.

This light dry snow sits atop the most recent crust layer formed and buried on Saturday 2/17. This crust has been reported up to 6600 feet by professionals in the region. While many layers are present in the snowpack, unstable snow has been relegated to the upper few feet.

Observations

On Wednesday, professional observations from the Mt Hood Meadows area indicated Loose-Dry avalanches were possible in steep terrain with several small natural Loose-Dry releases seen.

On Monday, Mt Hood Meadows patrol traveled into the above treeline area for the first time since the strong storm cycle. Surprisingly, they found a lack of wind slabs in terrain usually laden with them. The very cold temperatures may have limited slab formation in this area.

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 Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.