Be careful out there if you're riding in the next couple days...
From the NWAC:
Weather Service ID
Danger Rose for Tuesday
Danger Rose for Wednesday
Click here for complete definitions of the avalanche danger scale.
Forecast
Snowpack Analysis
In general, a perfect storm of avalanche conditions is unfolding in the Pacific NW early Tuesday morning, with lots of higher density snow or rain loading abundant potato chip like layers that exist through much of this fragile early season snowpack.
Recent weather effects: A series of cold storms from November 11-15 deposited 1-3 feet of low density snow, along with some faceting of the shallow snowpack. A strong storm with warming last Wednesday caused widespread avalanche activity and allowed a crust to form in many areas. Colder storms since Wednesday deposited an additional 1-2 feet of weak low density snow late last week while also producing further faceting and weakening of snow both near the ground and just above the crust. Some clearing, cold conditions, lighter winds and light showers last weekend allowed further weak near surface snow layers to form as well as areas of surface hoar. The most recent storm yesterday brought significant and generally denser new snow loading...ranging up to 12 to 20 inches...through slowly rising freezing levels and very strong winds.
Snowpack concerns: The current snowpack structure consists of many significant and potentially highly sensitive weak layers. Over the weekend, there were many reports of fantastic low density surface snow conditions over firmer old slabs or a crust layer along with reports of widespread surface hoar. Increasing wind slabs have now buried the low density surface snow, surface hoar and/or previous faceted snow, creating a highly sensitive and increasingly more dangerous snowpack. On morning avalanche control near Alpental, sensitive ski triggered slides were reported running far and fast, propagating through and releasing from some terrain with vegetative and terrain anchors.
As a result, the main avalanche concern involves newly formed slab layers and high rates of loading that should increasingly stress weaker snow, surface hoar, old slab layers and possibly some depth hoar as well as a weak rain crust/facet combination that formed last Wednesday in many areas below about 5 to 6000 ft. Although triggered slides may initially involve only the new snow received on Monday, as warming, loading and winds continue, progressively deeper weak layers should become involved with some larger and more destructive slides likely.
In general, this snowpack structure is primed for some rather large and very dangerous avalanches when loaded with additional large amounts of snow and rain, slow warming and strong winds expected into early Wednesday.
From the NWAC:
Weather Service ID
Danger Rose for Tuesday
Danger Rose for Wednesday
Click here for complete definitions of the avalanche danger scale.
Forecast
...AVALANCHE WARNING...
Tuesday and Tuesday night: High avalanche danger above 4000 feet and considerable below increasing and becoming extreme above 5000 feet and high below. Natural avalanches are certain with large to very large avalanches in many areas. Avoid all avalanche terrain.
Wednesday and Wednesday night: High to extreme avalanche danger continuing Wednesday morning, slowly decreasing Wednesday afternoon and night and becoming high above about 4000 feet in the north and 6000 feet in the south and considerable below.
Snowpack Analysis
In general, a perfect storm of avalanche conditions is unfolding in the Pacific NW early Tuesday morning, with lots of higher density snow or rain loading abundant potato chip like layers that exist through much of this fragile early season snowpack.
Recent weather effects: A series of cold storms from November 11-15 deposited 1-3 feet of low density snow, along with some faceting of the shallow snowpack. A strong storm with warming last Wednesday caused widespread avalanche activity and allowed a crust to form in many areas. Colder storms since Wednesday deposited an additional 1-2 feet of weak low density snow late last week while also producing further faceting and weakening of snow both near the ground and just above the crust. Some clearing, cold conditions, lighter winds and light showers last weekend allowed further weak near surface snow layers to form as well as areas of surface hoar. The most recent storm yesterday brought significant and generally denser new snow loading...ranging up to 12 to 20 inches...through slowly rising freezing levels and very strong winds.
Snowpack concerns: The current snowpack structure consists of many significant and potentially highly sensitive weak layers. Over the weekend, there were many reports of fantastic low density surface snow conditions over firmer old slabs or a crust layer along with reports of widespread surface hoar. Increasing wind slabs have now buried the low density surface snow, surface hoar and/or previous faceted snow, creating a highly sensitive and increasingly more dangerous snowpack. On morning avalanche control near Alpental, sensitive ski triggered slides were reported running far and fast, propagating through and releasing from some terrain with vegetative and terrain anchors.
As a result, the main avalanche concern involves newly formed slab layers and high rates of loading that should increasingly stress weaker snow, surface hoar, old slab layers and possibly some depth hoar as well as a weak rain crust/facet combination that formed last Wednesday in many areas below about 5 to 6000 ft. Although triggered slides may initially involve only the new snow received on Monday, as warming, loading and winds continue, progressively deeper weak layers should become involved with some larger and more destructive slides likely.
In general, this snowpack structure is primed for some rather large and very dangerous avalanches when loaded with additional large amounts of snow and rain, slow warming and strong winds expected into early Wednesday.
