Friday February 23, 2018
Cornice Fall, Wind Slab, Loose Dry
Travel & Terrain Advice
Seek low angle terrain and areas sheltered from the wind.
Ensure you a wide berth when travelling either above or below cornices.
Continued diligence when managing travel in avalanche terrain, small loose dry snow avalanches may start small but will quickly gain enough mass to push a traveler into terrain traps below.
The February 14th melt freeze crust located on all aspects and elevation continues to provide a bed surface for wind slab avalanches to slide on. This smooth and very strong crust will over the coming forecast period provide a sliding surface for future wind slab avalanches.
Wide spread and touchy to human triggers small size one wind slab avalanches have been reported. Predominately these wind slabs are found at ridge top and within open tree line terrain.
Isolated wind slabs on north aspects have been accidentally skier triggered, again these avalanches were small, size one.
Cornices are large and can be found on north aspects at both the treeline and the alpine. If triggered these could produce an avalanche big enough to bury injure or kill a traveler. Take the time to identify these features and ensure a wide berth when travelling either above or below them.
New snow fall with sustained and strong southwesterly wind will produce new wind slabs on features lee to the wind. Past wind slab and cross loading exist and wind slab will be wide spread on all aspects and found in the alpine, at tree line and below tree line. Wind slab avalanches when first formed will be touchy to human triggering and when trigger will produce large avalanches , size two.
New low density will be slow to settle as temperatures remain cool and as new snow fall continues through most of the forecast period. Loose snow avalanches will be touchy to human triggers and when triggered will begin small but will gain mass and have the possibility of producing large avalanches, size two. Small loose snow avalanches may not be big enough to bury a mountain traveler but may have enough mass to push them into a terrain trap below. Loose dry avalanches will be found on all aspects, in the alpine at treeline and below treeline.
Light and low density new snow of 15 cm continues to bond poorly to the valentines day melt freeze crust. In protected lee areas, 30 plus centimeters sits on this crust. Areas exposed to the wind such as ridge top at tree line and the alpine, the melt freeze crust is exposed and at the surface. The well establish crust provides a think and protective bridge above the snow below. The mid and lower snow pack remain well settled and strong.
|Surface||new low density snow|
|Upper||melt freeze crust from 30 to 90 cm thick|
Cool conditions persisted with overnight lows below minus 10 and up to 15 cm of new snowfall. Winds continued from the north west with variable velocity ranging from light to strong.
A series of winter storms will descend upon the region from the north, bringing to the area cool temperatures wind and continued snow fall.
Expected on western and interior zones up to a possible 50 centimeters of new snowfall over the 72 hour period with the eastern side of the island expecting half that amount. Winds will initially begin from the south west, becoming north and north west and will continue through the entire forecast period.
Friday 10 to 15 cm new snowfall. Temperatures -5 overnight rising to -2 mid day, winds strong north west. Freezing level 0 m rising to 900 m mid day.
Saturday 10 to 15 cm new snowfall. Temperatures -6 overnight rising to near 0 by mid day, winds moderate west. Freezing level 0 m rising to 700 m mid day.
Sunday 15 to 30 cm new snowfall. temperatures -5 rising to -2 mid day, winds light to moderate north west. Freezing level 250 m rising to 500 m mid day.
Posted on Friday February 23, 2018 by Jesse Percival