Avalanche Forecast
Regions: Mt Hood.
Further building or new wind slab should be the main avalanche problem on Wednesday. Be sure to read the forecast since wind slab may build on aspects where you don't expect it.
Detailed Forecast
Fair cold weather is generally expected to continue over the Olympics and Cascades on Wednesday. Low clouds will probably linger from the Columbia Basin to the Cascade east slopes and the east side of Mt Hood.
But expect locally strong east winds to develop over the Olympics and Washington Cascades Tuesday night and Wednesday. Therefore new or further building wind slab should be the main avalanche problem on Wednesday. This new wind slab should be found mainly on NW to SE aspects on Wednesday especially at exposed locations such as around Snoqualmie, Crystal Mountain, Paradise and White Pass. There should be quite a bit of recent snow available for transport. Watch for firmer wind transported snow and remember that stiffer wind slab has the potential to propagate to larger avalanches.
Although NW to SE aspects will be indicated in the wind slab avalanche problem diagram remember to watch for firmer wind transported snow on all slope aspects or cross loaded slopes especially in areas with varied terrain and modified wind directions. Older wind slab may also linger on other slope aspects.
Snowpack Discussion
Weather and Snowpack
A low pressure system moved south over western Washington on Saturday night followed by cold Arctic air. NWAC stations at Mt Hood had SW winds Saturday and 5Â inches of snowfall by Sunday morning.
An unusual moist reverse orographic east flow caused 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
A report via the NWAC Observations tab for Sunday indicates moderate compression test results and shear of moderate quality without propagation on the Solstice crust on a W-SW slope at 5600 feet.
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.
NWAC pro-observer Laura Green was on E-NE slopes on Elk Mountain on Monday and found minor wind transport in the above tree in the 4200-5400 foot range but no signs of instability.
Laura was at the Mt Hood Meadows Ski Area on Tuesday and also found minor wind transport in the above tree line.
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: South East, South, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1