Avalanche Forecast

A weak low pressure system crossing Oregon on Tuesday should produce light snowfall for the south Washington Cascades and Mt. Hood through early afternoon.

However, a deeper low pressure system approaching the Oregon Coast later Tuesday should cause shifting winds throughout the Cascade range including Mt. Hood by Tuesday afternoon that will begin to build new wind slabs on unusual aspects especially near and above treeline. Previous wind slab may linger on other slope aspects also in the near and above treeline bands. Watch for firmer wind transported snow on a variety of aspects if you push higher in the terrain Tuesday.

Storm slabs may be sensitive on Tuesday especially in areas where they overlie recently buried weak layers below treeline. Remember that recently formed surface hoar and surface faceted snow was observed in the below treeline band heading into the last storm cycle. Until more information is received, avoid slopes above terrain traps in the below treeline band where these weak layers may have been buried by the most recent snowfall. 

Weather and Snowpack

A cold and dry Arctic air mass was over the Northwest last week. The main weather event last week was a day or more of very strong east winds centered on Wednesday that went on a powder wrecking rampage, scouring windward slopes and re-distributing the snow to lee slopes while building sastrugi in other areas.

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. 

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. These deep slabs are unlikely to be triggered by a solo traveler, however, shallower wind slabs may be a different story. Settled and stable powder was found on wind sheltered terrain, where skiing conditions remained very nice.

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.