Wednesday January 24, 2018
Cornice Fall, Wind Slab
Travel & Terrain Advice
Give the big steep terrain a bit more time to settle and gain stability. As the weather settles down over the next few days we can start to explore but with very studious observations, cautious decision making, careful route finding and good travel techniques. Continue to stay clear of wind loaded NW-NE terrain like open bowls, steep convex rolls and fat zones below ridge tops in the alpine, treeline and open zones below treeline. Significant wind transport on Tuesday has plumped up these slopes and all they need is a human trigger. On a side note… the large snow fall Saturday into Sunday has increased the depth and hazard of open holes and tree wells significantly. Give trees some space and keep a wary eye out for open holes below treeline terrain. Ski with partners and meet up often.
Well its been an active few days for avalanche activity. Saturday into Sunday saw our huge storm which produced widespread natural avalanches (mainly on NW-NE asp) up to size 3 running in the new storm snow. Crown lines up to 50 cm deep. Monday avalanche control on Mt Washington saw size 1.5 to 2 avalanches (again on NW-NE asp) with explosives and ski cutting. Crowns up to 90 cm deep at treeline. Tuesday blizzard force winds were transporting very large amounts of snow to NW-NE aspects. Poor visibility limited observations, but we can certainly expect that a natural avalanche cycle took place on the steep lee terrain.
Winds have finally built up our cornices, in the alpine and treeline, to a point of concern. Remember to avoid travel below and on top of these features as they will be friable with the cool temps forecast and will have little support/strength. Ridges we have gotten used to sliding along this season will now be very different after this past storm cycle. We do not expect these cornices to fail naturally, but human triggering is likely up to size 2. Be cautious to the NE-NW sides of exposed ridge lines.
Massive winds and a lot of snow transport to NE-NW aspects in the alpine, treeline and open below treeline have left dangerous wind slabs in their wake. These slabs could possibly produce avalanches up to size 3 in isolated areas, are likely to create up to size 2 in specific areas and will certainly produce widespread size 1-1.5 avalanches on steep lee slopes and unsupported convex features. These avalanches may trigger naturally and will certainly trigger with human activity.
Since the obvious huge new snow fall last weekend….. Moderate to light amounts of snow have continued to fall in the forecast area. Mondays slight reprieve from the winter blast warmed direct solar slopes at treeline and below. Tuesday strong to intense winds from the SE-SW stripped snow from the windward side and we saw large amounts of transport to lee NW-NE aspects on all elevations.
|Surface||Very wind effected upper snowpack. Very large wind features/rollers/whales... in open areas. Widespread wind slabs on lee slopes|
|Upper||Moderate-firm wind pressed upper snowpack in open areas, Low density snow only in very wind sheltered zones|
|Mid||Lower density snow underlies these firm layers creating a potential layer of concern (hard over soft).|
The big story is the wind transport Tuesday. These strong to extreme winds from the SE-SW have significantly loaded NW-NE aspects at all elevations.
Light to moderate snowfall over the next three days (mainly falling in the evenings) and temps dropping. The new snow should be nice and light. Winds will mainly be moderate from the SE, but there is a bit of variable direction forecast so watch for potential loading on different aspects than we expect.
Posted on Wednesday January 24, 2018 by Bill Phipps