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Avalanche Forecast

Archived

Jan 2nd, 2017–Jan 3rd, 2017

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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

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 5 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.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.