Reactive wind slabs may exist in the treeline and the alpine. Watch and feel for signs of instability such as whumpfing, cracking, and recent avalanches.If you seek more sheltered areas at treeline you should consider that this is where the persistent slab has been most reactive in snowpack tests. Keep your terrain choices conservative and assess conditions while you travel.
New snow and strong wind may form fresh and reactive slabs on leeward slopes at upper elevations. Dry loose sluffing may be seen from steep slopes and terrain features.
Small avalanches may trigger a bigger avalanche by 'stepping down' to the weak and faceted crystals buried deeper within the snowpack.
Buried layers of surface hoar and facets exist 40-70 cm down and are showing reactivity in snowpack tests. Avalanches on this layer are possible where a cohesive slab (as opposed to loose, powdery snow) exists above this layer.
On Tuesday no new natural avalanches were reported but visibility was limited. Skier-controlled dry loose avalanches up to size 1 were seen. They ran in the recent storm snow and no deeper.
Last weekend, explosive control produced a large size 2.5 wind slab avalanche on a southeast aspect in the alpine. This avalanche gouged down to the faceted lower snowpack in its track and as a result, entrained a large amount of mass.
Looking forward, I suspect wind slabs will be reactive at upper elevations.
We have very limited observations in the field. If you do get out please consider reporting to the MIN.
Up to 15 cm of new low-density snow fell across the region by Wednesday morning. The new snow accompanied by changing winds (strong from the NW and now switching to the WSW) and slightly warming temperatures may form fresh and reactive wind slabs in the alpine and at treeline. This snow overlies a previously heavily wind-affected surface in open areas and many windward slopes may have been stripped back to early-season layers or rock.
30-60 cm of snow sits on top of a weak interface comprising of surface hoar and facets which showed reactivity in snowpack testing. The lower snowpack is sugary and faceted with a rain crust near the ground.
Total snowpack depths at treeline elevations are 50-80 cm.
Wednesday Night
Dribs and drabs overnight. Westerly winds 50-60 km/h at ridgetop. Temperatures are steady near -12 C.
Thursday
Cloudy with isolated flurries. Southwesterly winds 50-80 km/h at ridgetop. Temperatures slightly warming to -8 C and freezing levels valley bottom.
FridayMostly cloudy with light snow 5-10 cm. Strong to extreme southwest winds at ridgetop. Temperatures steady near -10 C.
SaturdayCloudy with 5 cm of new snow. Southwest winds are generally light with moderate to strong gusts at ridgetop. Treeline temperatures reach a high of -12 C.
More details can be found in the Mountain Weather Forecast.
