An unusual late season Atmospheric River enhanced storm passed through the region (4/6-4/7) with significant moisture, mostly in the form of rain (snow confined to ~10000’ to 11000’ and above) and accompanied by gale force winds. The heavy rain saturated the snowpack, resulting in extensive Loose Wet and numerous Wet Slab avalanches in the mid and lower elevations from McGee Creek north, and a few Wind Slab avalanches in the upper elevations Friday thru Saturday AM. The most avalanche activity occured primarily on N-NE aspects that had not gone through extensive freeze/thaw cycles and retained colder dry snow under the snow surface. The cold dry snow quickly became saturated by 1’ to 2.5” of rain, resulting in #’s D2-3 and a few isolated D3.5’s. As the rain eased off Saturday afternoon: excess free water began to leech out of the snowpack, while new inter-grain bonds began to form as temperatures began to fall and the snow began to refreeze. This allowed the avalanche hazard to fall back quickly Saturday as the snow began to adjust to the new load and stressors.
The 4/6-4/7 storm also was accompanied by strong to gale force winds in the upper elevations forming sensitive Wind Slabs on NW-NE-SE aspects with a D3 reported in the Sherwins. As time passes, these Wind Slabs are strengthening and are becoming increasingly stubborn to triggering but may still be encountered on NW-NE-SE aspects from ~10000’ and above. However, they’re becoming increasingly stubborn to trigger, especially by Monday.
The Wet Slab hazard has declined as heavy rains decreased Saturday, allowing the snowpack to begin consolidating and excess free water to drain, combined with a strong overnight freeze, this has essentially locked up the snowpack, preventing additional Wet Slab avalanche activity for the forecast period.
* Slide For Life conditions may exist on steep slopes where the snow is firm, especially during the AM hours. Ice Axes, Crampons, and a Helmet are recommended if traveling in steep or complex terrain.