Sun, Feb 9, 2020 - 6:46 PM
Broken Top Area / 9000'
Snow Conditions No Avalanche Activity
Ski or Snowboard
It was our first day of good weather in a long time, and I was hoping to get some information about the windslab problem in the Above Treeline elevation zone, since we have been lacking observations in that department lately.
I went out to Ball Butte first this morning. I was dismayed to see the extreme wind affected snow. It looked like the whole east side of the feature had been put in a panini press! Wind ridges and drifts were everywhere. I then went over to Broken Top Bowl, as the surfaces looked a little wind affected.
The temperatures stayed below freezing for most of the day, however, the solar input was strong. By 3:30, the trees just started dripping....barely. In the morning, the winds were Light in the bowl (up to 18mph), and on the ridgetops the wind was moderate ( 18-25 mph) out of the North and East. There was some stronger gusts at times. The blowing snow was evident as it was being picked up and moved from the North and East sides of the mountain, to the South and West aspects. The blowing snow would be considered Light in the avalanche world. As the day progressed, the blowing snow decreased.
In keeping with the most recent Avalanche Advisory for February 8-9, we went out expecting to see windslabs on SE-E-NE slopes, so we headed for what looked like the best snow (West and SW aspects), and hoping to avoid the windslab problem. On our approach, we were easily able to trigger at least one small windslab (picture attached) on a small convex roll, Near Treeline. The depth of this slab was about 20cm, and cracks shot out from my skis. However, interestingly enough, we found the most wind affected snow to be low in Broken Top Bowl. As we climbed higher, the overnight wind transported snow out of the North and East was deposited lightly on the old crust (from Feb 7) on the West and SW aspects (which had been previously scoured), and had no slab structure at all in this location. It was well bonded to the underlying rain crust. Hand shears in this surface layer showed poor quality shears.
The West and SW aspects had quickly become lee slopes overnight. Lucky us! This provided some great turns, and with no slab structure to the lightly wind deposited snow, we skied steep powder shots, from 30 to 40 degrees in steepness on these West and SW aspects. The depth of the new surface layer was anywhere from 10 -20 cm. No signs on any instability were observed inside the crater.
There were at least 2 previous slab avalanche crowns on steep South and Southeast facing aspects. These were small, and would be considered size 1, probably from Saturday's wind events.