Wednesday February 5, 2020
Wet Slab, Loose Wet, Wind Slab
Travel & Terrain Advice
Avoid steep terrain and exposure to terrain traps during the rain event forecast for Wednesday as a widespread loose wet avalanche cycle is expected. Carefully study how the new snow arriving mid day Thursday bonds to the old snow surface. Avoid wind loaded alpine and open treeline terrain after NW to SW winds Thursday push new snow to lee aspects. Watch for freshly buried refrozen loose wet avalanche debris in run out zones (its like skiing over hidden bowling balls)
A few minor loose dry avalanches and small wind slab pockets have reacted to ski cuts at Mt Washington up to size 1 on steep terrain N-W aspects at treeline.
Variable winds Sunday to Tuesday moved snow to cross loaded features, hollows, depressions and chutes on all aspects and elevations. These winds formed wind slabs that have a poor bond the frozen crust left after last Friday’s rain event. New rain arriving Wednesday into early Thursday will have the potential to turn these wind slabs into wet slab avalanches from size 1 to 3 in specific zones. These avalanches will possibly trigger naturally and are likely to trigger with human activity.
New low density snowfall over the past three days will saturate quickly as rain falls at all elevations all day Wednesday and into early Thursday. This rain event will result in widespread loose wet avalanche activity from size 1 to 2 that will certainly trigger naturally and very easily trigger with human activity, as the snow has a poor bond to the thick crust below.
As rain Wednesday into early Thursday tapers back to snow midday ….. Winds (moderate to strong from the NW to SW) will push this new snow to lee aspects in the alpine and treeline creating isolated wind slabs. These slabs may possibly result in avalanches size 1 to 1.5 with human triggering possible and natural triggering unlikely.
New snow over a semi supportive crust with some weakness below (low density snow). A moist well settled mid snowpack. The lower snpk is well bridged by layers above and is well settled also.
|Surface||6-30cm of new low density snow redistributed by var direction winds (deepest in the west, then north,least east)|
|Upper||A frozen rain crust (sometimes supportive other times breakable) with lower density snow underneath|
|Mid||Moist well settled snow with one thin crust layer mid and a huge thick crust at the base|
Light to moderate amounts of low density snowfall has fallen on a crust (that formed after the temps dropped, post the monsoon rains of Friday). Moderate to Strong winds from almost every direction have redistributed the new snow and formed wind slabs that have settled into cross loaded features, hollows, depressions and chutes. At ridge tops the winds have stripped the new snow away and exposed the crust. Nice snow still lies in wind sheltered zones but the crust is not far below.
Not looking amazing but things are looking up for the weekend…. and Backcountry Fest at Mt Cain (hint hint fundraiser for the bulletin).
Wednesday - 8 to 20mm of rain, moderate west winds, temps 1 to 5 degrees, freezing level 2700 dropping to 1700m
Thursday - mix of rain and snow 8 to 1 mm of rain followed by 3 to 5 cm of snow, winds light to moderate SW to NW, temps 1 dropping to -4, freezing level 1400 to 1000m
Friday - a lull in the precip early in the day followed by a heavy snow starting midday/evening and into Saturday morning, winds moderate SW rising to strong SSW, temps 0 to -4, freezing level 0 rising to 900m during the day.
Posted on Wednesday February 5, 2020 by Bill Phipps