In the last 36 hours, a very large natural avalanche ran off Schuylkill Ridge and impacted the flat valley below, while multiple human-triggered avalanches also occurred. Avalanche conditions are tricky. People are riding steep terrain in one area without observing signs of instability. Meanwhile, in other areas, often with similar characteristics, avalanches are occurring. In the big picture, dangerous avalanche conditions exist. If you don't want to roll the dice, these tricky conditions will require careful terrain selection and detailed snowpack evaluation. Lower-elevation southerly slopes offer the lowest risk of triggering a slab avalanche. If the sun begins to warm the snow surface on southerly-facing slopes today, a wet loose avalanche cycle will begin.
The sun is forecasted to make an appearance today. Wet loose avalanches will become possible to trigger on steep slopes that develop a few inches of wet snow on the surface of the snowpack. A wet loose avalanche cycle may begin if the sun comes out for a long period today.
The latest round of human-triggered slab avalanches were triggered on small facets below the recent storm snow. These avalanches have primarily released on northerly facing slopes, with average crown heights ranging from 1 to 2.5ft. Persistent slab avalanches can also release on weak layers in the middle or at the bottom of the snowpack, becoming very large and destructive. The newest generation of persistent slabs can be managed with slope angle choices and snowpack evaluation, while the deeper and older persistent slabs would most likely be triggered from areas that the snowpack thins near trigger points. Natural avalanche activity will continue to be possible on slopes that have active wind loading.
This notable natural avalanche ran Friday night or early Saturday morning. The avalanche debris pushed into the valley below. Schuylkill Ridge.
Northwest to west winds over the last few days have built thick slabs on the lee sides of terrain features. These slabs can release within the recent storm snow or step down to deeper weak layers where they overlap with the persistent slab avalanche problem. Last night, westerly winds averaged in the 20mph range with gusts into the 40's and 50's at 12,000ft. This avalanche problem commonly forms below ridgelines and on cross-loaded terrain features. Natural avalanches are possible on slopes with active wind-loading.
This small wind slab was human-triggered on Coney's yesterday.
Give the weekly summary a read for more details on the current snowpack and avalanche conditions heading into the weekend. You can view the video summary here, or the text summary here.
Avalanche conditions vary widely between the NW Mountain forecast area and the SE Mountain forecast area. Even some parts of the NW Mountain forecast area vary from other parts in the same forecast area. This is all due to the amount of snow that has accumulated since Thursday night. Local orographics have made for major variations in the amount of snow that has accumulated. Irwin has reported storm totals of 40” with 2.5” SWE. The Lake Irwin weather stations has also received 2.6” SWE in the same timeframe. An observer yesterday noted settled storm totals in the 12" to 16" range in the Anthracites near Ohio Pass which is only a couple miles away. The upper Slate River Valley also appears to be doing well with recent snow accumulations, and then Schofield Pass is running on the low end. CBMR has seen snow totals for the same period nearing 10”. A new persistent slab avalanche problem has developed in areas that have seen higher storm totals, while areas that have seen less snow are dealing with older persistent slab issues and new wind slabs.
The wind directions backs to the southwest tonight and may find a new fetch of snow to transport. We will have to see how those winds pan out. If winds increase into Monday from a new direction, they will continue wind-loading lee terrain features, and natural avalanches may remain possible. Those conditions will be re-assessed in the morning.
