Monday January 25, 2021
Persistent Slab, Wind Slab, Storm Slab
Travel & Terrain Advice
The recent storm snow has formed slabs in specific downwind areas that are reactive to human triggering. Be aware of the potential for loose dry snow avalanches in steel unsupported terrain. On Tuesday, with the continuation of the storm and potential wind, cross loaded and down wind areas will remain a concern to prioritize if venturing into avalanche terrain. Be conservative when travelling nearby 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.
On Tuesday, report of size 2 skier triggered avalanche within the forecast area. Additional snow and strong winds within the forecast region are such that we have increased the avalanche danger rating for Wednesday. Human triggered avalanches at the Alpine and Treeline elevation bands are considered “very likely” tommorow and potentially into Thursday.
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 firstname.lastname@example.org
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 North aspects. This wind slab overlies either a thick crust or a surface hoar layer, making it unstable. On Tuesday, the wind is forecasted to increase and switch to an easterly direction creating a cross-load wind slab problem in alpine and tree line features. 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 Tuesday.
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
10-30cm of wind affected new snow overlies an array of supportive melt freeze and rain crusts within the upper 50cm to 70cm of the upper snowpack. The crust at the Below Treeline elevation band is extremely supportive and providing difficult snowmobile and ski conditions in wind exposed areas where the new snow is no longer present.
|Surface||10cm to 30cm of new snow overlies surface hoar (PWL) in specific areas (wind sheltered terrain)|
|Upper||40cm 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|
The past week saw cool clear calm temperatures allowing for the growth of two separate (PWL’s) within the upper snowpack. A storm cycle on Sunday brought close to a foot of new snow to various parts of the forecast region and along with it a variable deposition of the new snow as winds in certain regions redistributed new snow to downwind areas.
On Monday, a weak low pressure system with periods of snow over the island. The highest accumulation of precipitation will likely occur from the central portion of the island and to the South. This low is expected to dissipate by Monday night. As the storm subsides, cold air from the interior will move to the coast which will be accompanied by strong outflow winds developing on Tuesday and into Wednesday.
Monday: 10cm to 30cm Snow, High - 3 Low -5, Light Winds from the NW, Freezing level 550M
Tuesday: 5cm to 10 cm Snow, High -1 Low -4, Moderate to Strong winds from the East, Freezing level 500M
Wednesday: 2cm to 5cm Snow, High -3 Low -8, Freezing level 400M
Posted on Monday January 25, 2021 by Ryan Shelly