Friday January 12, 2018
Wet Slab, Loose Wet, Wind Slab
Travel & Terrain Advice
The desire to play in the powder Friday will be strong, with the knowledge that rain and warm temps are on the way this weekend. Be very cautious, use conservative decision making and careful snowpack evaluations when traveling up or down into north-west facing wind loaded zones. If entering steep avalanche terrain and loaded bowls, proper avalanche gear, knowledge and education is a must. Take extra care and use safe techniques like skiing one at a time, safe zone to safe zone.
This weekend travel in avalanche terrain is not recommended! Significant weak layers exist in the snowpack that have shown failures in snow studies. These layers will wake up and become very active once the rain begins to fall to the very top of our mountains. Wet rain soaked avalanches are extremely powerful and present extreme danger when combined with terrain traps. Avoid exposure above cliffs, depressions, tree bands and steer clear of gully features. Remember wet avalanches tend to travel further than we expect and can run well into lower elevation bands and valleys. Also a friendly reminder that skiing is not permitted in closed terrain on Mount Washington. It is very likely that active avalanche control work will be underway over then next few days. Please for your safety and that of the avalanche teams, stay out until gates are opened and do not cut under rope lines.
Thursday saw a marked rise in avalanche activity/sensitivity by both natural and human triggering. Wind slabs up to size 1.5 were very easily triggered while skiing treeline and below treeline N-E aspect terrain on steeper pitches and unsupported convex features. The majority of these slabs ran down 5-25 cm on the January crust. Natural activity was also seen on steep north facing treeline terrain. Visibility has limited any alpine observations.
The rain may also trigger wet slab avalanche activity on north west aspects where our wind slabs built Thursday-Friday. It is likely to very likely that these wet slabs could be triggered by natural and or human activity. These slabs will be in the alpine and treeline and have the potential to be up to size 3.
Sadly, significant rainfall is forecast for our mountains this weekend well up into the alpine. This rain will almost certainly result in loose wet avalanche activity that will be easily triggered by human activity and natural triggering, and may produce avalanches up to size 1.5. Loose activity will be at all elevations and aspects.
Snowfall Thursday and the forecast storm Friday, will come with strong to moderate south east winds. These winds will create wind slabs in the alpine, treeline, and open pockets below treeline on the lee (north west aspects). These slabs will be widespread in the alpine, on specific terrain in the treeline, and on isolated terrain features below treeline. The slabs will be touchy, are very likely to almost certainly going to be triggered naturally and will be reactive to human activity. The slabs have the potential to be up to size 2.
Strong to moderate south east winds have added to wind slabs on the north to west aspects in the alpine and treeline. All this new load (in some areas up to 60 cm) is sitting on the January 6th rain crust which has shown significant weakness and failures in tests (producing moderate non planar results)
|Surface||New low density snow in wind sheltered zones. Exposed areas have wind pressed slab properties but still ski well.|
|Upper||New snow everywhere with a thin non-supportive crust, approximately 15-30 cm down on below treeline and treeline terrain from Monday's warm spike.|
|Mid||The new snow and crust buried on Jan 6th is now bridging and almost eliminating concerns surrounding the mid Dec and mid Nov crusts. The moist mid snowpack seams very stable producing only hard results in tests on the Dec crust.|
Strong to moderate winds from the south-east accompanied the new snowfall (up to 15cm) Thursday. Freezing levels have stayed low (below 1000m) in the east but did jump up to 1300-1400 m in the west and north.
Moderate to strong south east winds through the forecast period. More new snow for Friday with rain to the top of our mountains for Saturday, easing Sunday. Very high freezing levels and temps into the weekend.
Fri - 5-20 cm of new snow. Winds moderate to strong south east. Freezing levels of 600-1200 m
Sat - 10-20 mm of rain. Winds moderate to strong south east. Freezing levels of 1200-3000 m
Sun - 0-2 mm of rain. Winds moderate to strong south east. Freezing levels of 2300-3000 m
Posted on Wednesday January 17, 2018 by Bill Phipps