Thursday January 28, 2021
Persistent Slab, Wind Slab, Storm Slab
Travel & Terrain Advice
The recent storm snow and winds have formed soft slabs in specific (west facing slopes) in downwind areas that are reactive to human triggering.
Be aware of the potential for loose dry snow avalanches in steep unsupported terrain.
On Wednesday, with the continuation of the storm and wind, cross loaded and down wind areas will remain a concern to prioritize if venturing into avalanche terrain.
Be cautious when travelling nearby or adjacent to cornices as they are generally unstable (very much so at this time during a storm/wind cycle).
Maintain a close eye on the transition areas between wind scoured and snow loaded areas as these zones can be good areas to initiate avalanches at this time.
Simple Avalanches Terrain ( terrain generally under 30 degrees) would be the place to recreate at this time given the dynamic weather we are experiencing at this time.
On Tuesday Jan 26 and Wednesday Jan 27, reports of size 1 and size 2 skier triggered avalanches within the forecast area. Avalanches appear to be soft slab in nature and are not showing hard slab properties that could promote propagation (which is a good thing). Mount Washington ski patrol reported several “several” controlled avalanches being initiated, also soft slab in nature. For this reason we have downscaled the avalanche hazard now that the storm has passed. Human triggered avalanches at the Alpine elevation band is considered “likely” for Thursday and Friday.
Thank you Griffin Fisk, Theron Finley, Sportnewk, Gilbert and Andrew S for posting to the MIN and Joe, Cliff, Abby Rutherford, Kalen and Tim Plante for sending OBS in to email@example.com
This forecast brought to you collaboratively by shadow forecaster Dave Kallai and forecaster Ryan Shelly
There hasn’t been any activity, but we are still concerned about our two persistent weak layers (PWL) that form our persistent slab problem. Since this layer isn’t currently reactive to skier traffic, the likelihood may be low. However, this layer is deep in the snowpack, and with an increased load such as a cornice fall, it could be triggered, creating a large avalanche.
Location: Found at all elevation bands and on multiple aspects.
Possibility: Unlikely to Possible from natural and human triggers.
Size: If triggered, expect these avalanches to be large enough to bury a person (size 2-3).
The recent winds have produced Wind slabs that can be found predominantly on NW aspects. This soft snow wind slab overlies either a thick crust or a surface hoar layer, making it unstable. The stability hazard of this problem is improving and consolidating to pre-existing snowpack. On Saturday however, winds will increase and exacerbate the upper snowpack with new wind slab problems in downwind areas. Location: All aspects at alpine and treeline.
Possibility: Triggering of this avalanche problem is “possible to “likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” to “unlikely” depending on the elevation band.
Size: If triggered, expect these avalanches to be large enough to bury a person, size 2.
The recent storm created storm slabs in areas less exposed to the wind. This is present in all aspects and elevations.
Location: All aspects and at all elevation bands into Thursday.
Possibility: Triggering of this avalanche problem is “possible” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are unlikely depending on the elevation band. The storm slab hazard will increase on Saturday with additional high precipitation rates in specific areas on Vancouver Island.
Size: If triggered, expect these avalanches to be large enough to bury a person, size 2
20-50cm of loose powder snow ( and in specific downwind areas a soft slab of new snow) overlies an array of supportive melt freeze and rain crusts within the upper 60cm to 80cm of the upper snowpack. The crust at the Below Treeline elevation band is now buried and the newest powder snow is sensitive to triggering.
|Surface||20cm to 40cm of loose dry powder snow overlies surface hoar (PWL) in specific areas (wind sheltered terrain)|
|Upper||20 to 50cm below the surface exists a melt freeze crust with facets (PWL) resting above this crust|
|Mid||Generally well settled with several melt freeze crust layers|
|Lower||Well settled and well bridged and includes a 10cm thick layer of large facets (Dormant PWL)|
New snow, cold temperatures and some wind affect have made for outstanding snowmobiling and skiing/snowshoeing since the storms arrival several days ago. As a result of all the new snow, it appears that avalanche activity is occuring within the upper 20cm to 50cm of the upper snowpack. Expect this problem to increase as additional new snow arrives into the weekend for specific areas within the forecast region.
More snow and consistent cooler temperatures are incoming for the next several days. Expect the weather to become a bit more aggressive on the weekend as strong winds and strong precipitation rates arrive Saturday January 30th. Light precipitation for the East and North end of the forecast region while the West and South end of our bulletin area stand to receive strong amounts of snowfall.
Thursday: 1cm Snow, Moderate winds from the East shift to Light East winds at mid-day, Freezing level 750M
Friday: 2cm to 10 cm Snow, Light SE winds shifting to Moderate SE winds at mid-day, Freezing level 800M
Saturday: 10cm to 40cm Snow (strong precip amounts are forecast for the west side of the forecast region, while lighter precip rates (10cm Snow) are forecast for the East side and North end of the forecast region, Strong SE winds, Freezing level 850M
Posted on Wednesday January 27, 2021 by Ryan Shelly