Avalanche Forecast

A relatively brief (6 hour) period of heavy rain and snow in the above treeline band will be changing to snow showers later Monday night and will continue on Tuesday. Strong SW winds should decrease slightly on Tuesday. The colder temperatures will allow wet snow to begin to refreeze.

Fresh winds with the new snow will form small to large wind slabs near and above treeline, which will be touchy on Tuesday. Avoid wind-loaded terrain as it won't take much new snow to redistribute the snow to form a large slab. Give potentially wind-loaded terrain near ridges a wide margin for error on Tuesday.

Older wind slabs which which were triggered by large explosives over the past weekend are likely very stubborn to trigger, but may still be reactive to cornice or other large triggers on Tuesday. A facet/crust combo exists and this layer has produced very large avalanches, so avoid travel on or connected to a large avalanche path Tuesday. While these avalanches may be unlikely, they will be unsurvivable.

Large storm slabs forming Monday night in the above treeline band will likely be sensitive to human triggering on Tuesday. Avoid steeper terrain (>30 degrees) and convex or unsupported slopes at higher elevations. At lower elevations where a rain crust will be refreezing, expect storm slabs to be possible if heavier snowfall rates are seen within the shower activity. Make more conservative terrain choices where new snow exceeds 8" on top of the recent crust.

A relative break in the action was seen from late morning Sunday through Monday after a long and stormy period which has impacted the Mt Hood area since January 17th leaving 30 inches of settled storm snow over the most recent crust layer. Saturday and Sunday featured more intense precipitation, significant warming temperatures, and strong winds created very dangerous avalanche conditions and natural avalanches in many areas.

The break in the weather allowed good visibility of multiple very large artillery-triggered wind slabs which entrained lots of wet snow and even in one case knocked down timber.

Rain on Saturday morning was followed by cooling, creating a thin, breakable crust in some areas.

Winds throughout this active weather pattern redistributed snow forming deep and firm wind slabs on lee slopes near and above treeline.  

Observations

Mt Hood Meadows Pro Patrol Sunday reported multiple very large artillery-released avalanches with very deep crowns up to 12 ft range, running on steep NE and E-NE terrain above treeline and travelling very long distances, in one case snapping 20+ year old trees. Snow pits in the 5000 and 7000 ft range identified 1 mm rounding, wet facets on top of a 1/18 freezing rain crust as the likely weak-layer/bed surface for these very large slides. Given the large amount of recent wind transport, the depth of this layer varied widely.

A Mt. Hood Meadows Patroller provides scale for the sidewall of one of these very large explosive-triggered avalanches on Mt. Hood.

Mt Hood Meadows Patrol Saturday reported sensitive storm slabs which were entraining snow as they ran. A thin breakable rain crust formed in the morning to 5500 feet. By mid-day additional snow was falling at most elevations.