Register for an account and never miss a forecast again!
RegisterRegister for an account and never miss a forecast again!
RegisterJan 9th, 2017–Jan 10th, 2017
Olympics.
Shifting and increasing E or NE winds Tuesday afternoon will begin to build new wind slabs on unusual westerly aspects especially near and above treeline. Also avoid slopes above terrain traps in the below treeline band where recently formed weak layers may have been buried by new snow.
A weak low pressure system crossing Oregon on Tuesday should produce periods of light snowfall mainly along the north slopes of the Olympics.
However, a deeper low pressure system approaching the Oregon Coast later Tuesday should cause shifting and increasing E or NE winds throughout the Cascade and Olympic ranges by Tuesday afternoon that will begin to build new wind slabs on unusual westerly 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.
Generally shallow storm slabs should be less sensitive on Tuesday except 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.
Continue to identify the 12/17 buried PWL in snowpits and avoid areas where the overlying snowpack is shallower such that affecting this layer would be more likely.
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 Sunday and again Sunday night left temperatures see-sawing near or above freezing for areas away from the Passes including Hurricane Ridge. 6 inches of new snow was reported by NPS staff Monday morning at Hurricane Ridge.
Recent Observations
NWAC pro-observer, Matt Schonwald was in the field with NPS rangers in the Hurricane Ridge area Friday, 1/6. Matt traveled to Steeple Rock on the Obstruction Peak Road. The persistent weak layer from 12/17 was evident in the two distinct areas where snow tests were performed. The layer ranged in depth from 110 cm on SSW aspect to 135 cm on NW aspect. While reactive in deep snowpack tests and PST's, stiff overlying layers and the fact the layer is deeper than 1 meter make human triggering of this layer unlikely. Of greater concern were the areas of recent wind slabs on a variety of aspects. There was no evidence of very recent avalanches, in that terrain, but older slides were seen, likely releasing during the strong wind events earlier in the week.
Matt also relayed to us photos of a skier triggered hard wind slab avalanche on a 35 degree, W-NW slope at Hurricane on Saturday. Apparently the skiers that triggered the avalanche were not caught.
Skier triggered hard wind slab avalanche on a 35 degree, W-NW slope at Hurricane on Saturday. Photo by Gary Holmquist.