Avalanche Forecast
Regions: Mt Hood.
The recent shift to NE winds makes new wind slab most likely on NW to SE aspects on Tuesday Remember that stiffer wind slab has the potential to propagate to larger avalanches. But don't let your guard down and watch for wind transported snow on other slopes as well.
Detailed Forecast
A weakening upper trough should linger over the Northwest on Tuesday. Meanwhile a cold Arctic air mass will slowly push further south over the BC-Montana area causing cold offshore surface flow over the Northwest. Alpine NE winds should ease a bit but not go away on Tuesday. Low clouds from the Columbia Basin will still probably affect the south Cascades on Tuesday.
The recent shift to NE winds makes new wind slab most likely on NW to SE aspects on Tuesday. This should be most likely in the south Cascades and Mt Hood. Watch for firmer wind transported snow mainly on lee NW to SE slopes at exposed alpine locations. Remember that stiffer wind slab has the potential to propagate to larger avalanches. But since winds have shifted the past couple days don't let your guard down and watch for wind transported snow on other slopes as well.
New storm slab is also possible at Mt Hood due to recent significant snowfall ending Monday morning.
Snowpack Discussion
Weather and Snowpack
A low pressure system moved south over western Washington on Saturday night followed by an influx of cold Arctic air. NWAC stations at Mt Hood had SW winds Saturday and 5Â inches of snowfall by Sunday morning. A colder Arctic air mass began to move into the Northwest.
High surface pressure and moisture east of the crest caused east flow and snow mainly in the central to south Cascades Sunday afternoon and night. NWAC stations at Mt Hood had a shift to NE winds and another 10-12 inches of snow on Monday morning and further cooling as the Arctic air mass further moved into the Northwest.
Recent Observations
The Mt Hood Meadows pro-patrol on Monday reported that the recent wind shift was moving snow to S-W slopes. On avalanche control on Monday morning sensitive 4-6 inch storm slabs were released by skis on most test slopes. Deeper storm slab to about 2 feet was expected in loaded areas which could release to the Solstice crust. The shift to NE winds as also building new local soft 8-24 inch wind slab on S-W slopes.
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1