Monday February 11, 2019
Wind Slab, Loose Dry
Travel & Terrain Advice
Travel in the Alpine on South facing terrain will likely result in triggering an avalanche. Stick to lower angle terrain if venturing into the Alpine and avoid South Facing terrain as windslabs will remain a concern for the next 48 hours. Steep unsupported terrain continues to provide ‘sloughing’ as size 1 avalanches. Continue to pick careful routes that will not result in exposure or vulnerability to terrain traps as this loose dry snow remains unconsolidated and relatively easy to initiate on steep terrain.
Several reported skier triggered avalanches around Mt Cain this weekend. These avalanches were initiated on wind slabs (Two skier triggered size 1 avalanches and one skier triggered size 2 avalanche) in leeward (south facing) terrain in the Alpine. The winds have now subsided on the North End of the island, however today, Mt Washington was hit with moderate to strong winds and 30cm of new snow. Leeward terrain (south facing) below ridges, mountain tops, terrain depressions that can collect snow and areas below cornices ALL on south facing slopes will be areas to avoid as they will most likely produce size 1 and size 2+ avalanches as a result of the significant 30+cm of new snow and winds that occurred today.
South facing terrain in the Alpine will continue to produce avalanches in the size 1-2+ range as a result of new powder snow (precipitation) and moderate to strong winds.
Steep unsupported terrain in areas protected from winds will continue to produce size 1 avalanches as a result of the unconsolidated powder snow that has not yet bonded to the melt freeze crust down 20-40cm from the surface of the snowpack.
Depending on aspect and exposure to winds, the terrain has between 20-40cm of fresh powder snow. On south facing terrain, the winds have created a soft slab avalanche hazard ranging in depth from 20-40cm. We should expect these wind slabs to stabilize by mid week (Wednesday). A secondary problem is the the light dry powder snow sitting on steep and unsupported terrain in areas unaffected by the recent winds. Size 1 avalanches continue to be produced as ‘sloughs’ on steep unsupported terrain. Generally speaking, the snowpack is very well consolidated and bonded except for the upper surface storm snow and wind driven instabilities which can be found on south facing terrain.
|Surface||20-40 cm of wind slab or in wind protected areas 40cm of dry powder snow|
|Upper||Thick 10cm melt freeze crust|
|Mid||Well bonded midpack that does include two weaker (PWL) layers (Facet layer and Surface Hoar layer) both un-reactive to testing|
Strong winds in the 70-80km/h range have affected the north island earlier in the weekend. The mid island received strong to moderate winds in addition to 30cm of new snow around Mt Washington until this evening (Sunday Feb 10)
Monday: 3cm - 6 cm of new snow, Temperature -15 to -5 degrees, Moderate Winds from the East North East, Freezing Level 0 M
Tuesday: 10cm - 20 cm of new snow, Temperature -11 to -4 degrees, Moderate Winds from the East, Freezing Level 130M
Wednesday: 1cm - 4 cm of new snow, Temperature -12 to 0 degrees, Light Winds from the North East shifting to South, Freezing Level 800M (she’s warming up!)
Posted on Monday February 11, 2019 by Ryan Shelly