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RegisterJan 2nd, 2017–Jan 3rd, 2017
Stevens Pass.
The recent shift to NE winds makes new wind slab most likely on NW to SE aspects on Tuesday especially from Snoqualmie south. Remember that stiffer wind slab has the potential to propagate to larger avalanches.
A weakening upper trough should linger over the Northwest on Tuesday. Meanwhile a cold Arctic air mass will slowly push further south over the BC-Montana area causing cold offshore surface flow over the Northwest. Alpine NE winds should ease a bit but not go away on Tuesday. East winds could remain pretty strong at Snoqualmie. Low clouds from the Columbia Basin will still probably affect the south Cascades on Tuesday.
The recent shift to NE winds makes new wind slab most likely on NW to SE aspects on Tuesday. This should be most likely from Snoqualmie south. Watch for firmer wind transported snow mainly on lee NW to SE slopes at exposed alpine locations such as around Snoqualmie, Crystal Mountain, Paradise and White Pass. Remember that stiffer wind slab has the potential to propagate to larger avalanches. But since winds have shifted the past couple days don't let your guard down and watch for wind transported snow on other slopes as well.
The 12/17 PWL persistent slab problem is becoming more deeply buried and less sensitive in snowpack tests and has been removed from the avalanche problem set.
Weather and Snowpack
A low pressure system moved south over western Washington on Saturday night followed by an influx of cold Arctic air. NWAC stations along the west slopes had W-SW winds Saturday and 5-13 inches of snowfall by Sunday morning. A colder Arctic air mass began to move into the Northwest.
High surface pressure and moisture east of the crest caused east flow and snow mainly in the central to south Cascades Sunday afternoon and night. NWAC stations along the west slopes had a shift to NE winds and another 0-10 inches of snow on Monday morning with the most snow in the central to south part and further cooling as the Arctic air mass further moved into the Northwest.
Recent Observations
Consistent observations were received on New Year's Day from three NWAC pro-observer's out enjoying the after champagne, champagne powder! Reports from the Mt Baker area, Stevens Pass and the Alpental Valley, Snoqualmie Pass, all reporting amazing deep, low density surface conditions, providing excellent downhill skiing, if after tough up hill trail-breaking. No triggered slab releases were noted with mostly no slab formations encountered with a right side up snow profile. A good bond to the old snow surfaces was noted with any crust layers buried fairly deeply and unreactive in tests (Solstice crust at Snoqualmie buried 90 cm on average). All observers noted extensive sluffing on steep descents, mostly the upper several inches of snow. Not necessarily a major concern, however, these conditions should persist in wind sheltered terrain with the continued cold temperatures.
The Alpental pro-patrol performed cornice missions Saturday and easily dropped soft cornices that released only shallow slides within the storm snow on the slopes below, not involving the deeper crust involved in earlier cornice failure Friday.
The NPS ranger at Paradise on Monday reported low visibility with significant snow transport to SW-W slopes on Monday.