[Forecaster Comment: We received two separate observations from this avalanche occurrence, where both parties were at the scene. We are publishing a single observation, with separate comments from each observer. We also added video coverage submitted by Matt Buranich]
Saw this skier triggered avalanche while hiking out of South Monitor and went to investigate it. Looked to be the fifth person to ski the slope, and looked like he hit a thin spot in the snow pack and triggered the slide. Luckily he triggered it right on the flank and was not in danger of burial. The debris pile was at least 20ft deep, my probe would not reach the ground fully extended. The slide looked to have taken out the snow from our last two little storms and the bigger storm from yesterday, sliding on the hard crust from the warm spell before that. The boarder was about a quarter of the way down the slope when he triggered it and it fractured across and up-slope of the trigger point. Luckily he wasn't in the gut of it or it most likely would have had not ended well.
Three separate parties arrived at the top of West Monitor in quick succession. My party of two skiers descended first, without incident or any signs of instability. Shortly thereafter, while my party was ascending the skin track at the north end of the bowl, the second party of two also skied the bowl without incident. While the second party was at the base of the bowl, a solo snowboarder, the fifth rider to enter, remotely triggered an avalanche. (I gathered the following information from the boarder and the members of the second party). The avalanche started above and to the north of him, when he was approximately 30% through his run. The party below yelled up to alert the boarder, who immediately bee-lined it to the bottom. The avalanche fan caught up to him at the bottom but he stayed upright, having only been partially buried over his boots. The boarder lost his poles, which he dropped to hasten the bee-line, but was happy to be alive and uninjured. The party of two at the base of the bowl during the avalanche were also lucky to have been able to side step the deposition at the toe.
Other Observations. This is a repeater avalanche, the first two times being in late December and mid January. Prior to yesterday’s storm, West Monitor had been heavily tracked. In spite of the wind that accompanied the storm, the new snow had no signs of slabbing or instability. Cornice cuts on the ridge yielded only minor sluffing. The avalanche ran completely in the new snow and did not step down into the old faceted layers. In retrospect, although the the new snow had no visible signs of slabbing from yesterday’s storm, there were red flags: 1. West Monitor is a repeater. No repeater is to be trusted until it’s bed surface is pouring out of your faucet in the Spring; 2. West Willow (another infamous repeater) had slid during the storm or shortly afterwards. We had observed the presence of the Willow slide earlier in the morning; 3. The avalanche advisory reported soft slab avalanche from control work in the same area with similar aspect, angle and elevation (although during the storm); 4. West Monitor had been receiving full sun throughout the morning, and this is a factor later in season (is it really later in the season, already!!!); 5. As I stood at the top of the bowl discussing the health of a buddy who had recently been caught and seriously injured in an avalanche, I had an instinctive twinge of reservation about skiing the bowl. Although me and my partner skied the bowl, ourselves, without incident, we realize now that we were just mighty lucky, as were the second party and the boarder who just happen to draw the short straw. I will be trusting instincts and staying away from repeaters for the remainder of 2018.
[Forecaster Comment - Excellent writeup and retrospection of considering dropping into avalanche terrain. Although this may have been a repeater from earlier in the season, the slide ran on a stout sun crust that formed during the week of February 5. Two small storms (Saturday Feb 10 and Monday Feb 12) fell on top of this crust, followed by the larger storm on Thursday Feb 15. This avalanche took out the storm snow from these three recent storm events, and did not run on weaker faceted layers that would be present in slide paths from repeater avalanches.]