Avalanche Forecast

High pressure should cause a clear, cold night Wednesday and a sunny day Thursday with light winds and cold temperatures. There has been low density snow available for recent transport and with the expected cold temperatures, wind slabs will be slow to settle and stabilize. 

The fresh wind slabs could be found on a wide variety of aspects due to the recent shifting winds, from easterly to southwesterly. Therefore, watch for cross-loaded slopes, especially above treeline due to westerly winds higher on the volcano creating wind slabs on a variety of aspects. Watch for firmer wind transported snow and avoid freshly loaded slopes in all elevation bands.

Small loose dry avalanches are possible in steep wind sheltered terrain, but will not be listed as an avalanche problem. 

East Slopes North - Canadian Border to Lake Chelan, East Slopes Central - Lake Chelan to South of I-90, East Slopes South - South of I-90 to Columbia RiverDay 1 Detailed Forecast

A low pressure system crossing Oregon Tuesday night will cause a sustained round of moderate easterly winds through Wednesday morning. Light snowfall should taper off in the morning for the southeast and central-east Washington Cascades with clearer conditions expected over the northeast Cascades. Winds will not be nearly as strong as the east wind event of last week, but there is low density snow available for transport and cold temperatures Wednesday will help preserve any new instabilities.

New wind slab should build through Wednesday morning due to easterly winds depositing snow primarily on lee westerly aspects. Transport winds will be more out of the northeast in the Washington Pass zone. However, also watch for cross-loaded slopes and lingering wind slab on a variety of aspects. Watch for firmer wind transported snow and avoid freshly loaded slopes in all elevation bands.  

Small loose dry avalanches are possible in steep wind sheltered terrain but will not be listed as an avalanche problem. 

Continue to identify the 12/17 and less deeply buried PWLs in snowpits and avoid areas where the overlying snowpack is shallower where affecting these layers would be more likely.

 

 

 

 

Weather and Snowpack

A cold and dry Arctic air mass was over the Northwest last week. The main weather event during this cold snap was a day of strong east winds last Wednesday that created widespread variable snow surfaces by scouring windward slopes and re-distributing the snow to a variety of aspects.

Reports indicate the winds eliminated most of the faceted surface snow and surface hoar that formed in the near and above treeline during the cold weather. But these weak surface crystals were still reported below treeline prior to snowfall that fell over the weekend.

A pair of warm fronts moving through the PNW Saturday and again Sunday left temperatures see-sawing near or above freezing. The Mt. Hood Meadows base station saw a jump of over 20 degrees Saturday evening as low level easterly flow finally abated allowing milder Pacific air to move in. 8 inches of snow fell through Monday morning with another 5 inches accumulating in the Mt. Hood area at NWAC stations through Monday afternoon. 

Mt. Hood was stacking up the new snow Tuesday with another 15-20 inches falling Monday night through Wednesday midday. Winds were generally light to moderate in this storm, but E winds increased mid-mountain Tuesday afternoon, then switched to SW Wednesday.  

Recent Observations

NWAC pro-observer Laura Green was at the Mt Hood Meadows Ski Area on Thursday following some of the strongest winds experienced on Mt Hood for a very long time. She found a mix of wind sculpted conditions, ranging from deep hard slabs, likely 1-2 meters or more in depth as well as scoured slopes to crust layers, sastrugi, and a thin melt-freeze sun crust on many south aspects. 

Laura was out again on Friday in the Mitchell/Iron Creek area in the 4200-6000 foot range and found hard slab drifts from the high wind event of 1/4 even below treeline, and in reverse of what is usually present due to the east winds. She reported lots of variation in surfaces - wind hardened snow, sastrugi, bumpy ice, settled powder and tree debris. But no signs of instability were observed.

Following the new snow Sunday night, Mt. Hood Meadows pro-patrol found generally stubborn 6-12" wind slabs releasing on N and E aspects above treeline during control work Monday morning. While most slabs released within the new storm snow, some deeper pockets broke down to either a thin freezing rain crust formed over the weekend or the previously scoured surface from late last week. 

On Tuesday, the Meadows pro-patrol reported generally good skiing and riding conditions with the new snow. 6-12" storm or wind slabs were soft but could be triggered above treeline in specific areas. The patrol reported cracks propagating through the new snow, but in many areas the lack of a cohesive slab prevented avalanches from releasing. 

On Wednesday, the Meadows pro-patrol did not venture above about 6600 feet, due to white out conditions. Below this elevation, in the mostly below tree line band, sheltered slopes were maintaining right side up powder conditions that lacked any slab structure, providing excellent conditions.