Monday April 9, 2018
Wind Slab, Loose Wet, Cornice Fall
Travel & Terrain Advice
use terrain features to avoid wind loaded areas
avoid south aspect terrain if and when the sun comes out
Identify terrain traps and avoid as even a small avalanche will gain mass and pose a potential threat
Over the past three days , numerous natural avalanches observed up to size 1.5 loose and wet on all aspects and primarily at treeline and the alpine. Ski cutting and explosive testing reveled the upper snow pack to be touchy to skier traffic and easily trigger. Once trigger the wet upper snow pack easily gained mass and even a small avalanche posed a threat to mountain travelers.
New heavy snow fall Tuesday with sustained and strong southeasterly wind will produce new wind slabs on features lee to the wind. Current wind slab and cross loading exist and wind slab will be specific to western aspects and found in the alpine and at tree line. Wind slab avalanches when first formed will be touchy to human triggering and when triggered will produce large to very avalanches (2 to 3).
During this forecast period expect solar effect, rain on snow and warming temperatures at all elevations and aspects to further destabilize the already unconsolidated upper snow pack. These factors will produce small loose wet natural avalanches that will effect travelers exposed to terrain traps such as cliffs . These avalanches will form quickly when the sun comes out, temperatures warm or rain falls on new snow and are and will be very touchy to human traffic. If triggered these hazardous avalanches will gain mass producing avalanches large to very large in size (2 to 3) and will be able to bury, injure or kill a mountain traveler.
Expect already large cornices to continue to grow on Tuesday becoming fragile and very touchy to human triggering. Cornices are located on predominantly north aspects at both the treeline and the alpine and if triggered these could produce a large avalanche big enough to bury injure or kill a traveler (2). Take the time to identify these features and ensure a wide berth when travelling either above or below them.
Heavy precipitation in the form of rain and wet snow has unconsolidated the upper snow pack. and the surface remains warm and wet. At treeline consistent observations found the snow pack to be at zero degrees down between 40 and 60 centimeters and foot penetration would vary between 45 centimeters and 100 centimeters dependent on aspect and elevation. The March 22 melt freeze layer is deep enough that it would only be trigger by a very large trigger and is not dormant but currently nonreactive. Below this a well settled and dense snow pack exists
|Surface||wet and unconsolidated|
|Upper||wet and unconsolidated|
|Mid||March 22 melt freeze crust suspect down over a meter|
Warm and wet conditions persisted and the forecast areas received over 65 mm of rain fall. Winds where strong from the south east and during Saturday night freezing levels dropped to the 1300 meter mark and precipitation fell as wet snow.
Initially a weak ridge today will bring some relief from pacific warm fronts and some clearing with very little precipitation forecast and light wind. Beginning Tuesday a low pressure to the west of the region will bring to the area, heavy precipitation both in the form of rain and snow, and strong south east winds.
Monday no new snowfall. Temperatures 2 overnight rising to 6 mid day, winds light south east. Freezing level 1600 m rising to 2000 m mid day.
Tuesday 20 to 50 cm new snowfall 20 mm of rainfall. Temperatures 3 overnight rising to 4 by mid day, winds strong south east. Freezing level 1500 m dropping to 1000 m mid day.
Wednesday 10 to 20 cm new snowfall, 10 to 20 mm of rainfall. temperatures 0 rising to 1.5 mid day, winds light to moderate south east. Freezing level 1200 m.
Posted on Monday April 9, 2018 by Jesse Percival