Quick report
Today our touring party observed clear skies and big views in the Flathead Range. The temperatures warmed quickly from -7F at the trailhead into the mid 20sF by 1pm @7000' and winds were calm. These clear skies and warming temperatures initiated loose dry, then wet loose avalanches that had the potential to trigger other larger deeper avalanches and we began to see natural activity around 11:30am. We observed no obvious signs of instability on shaded aspects until unintentionally triggering a large avalanche near the end of the day. This avalanche was a near-miss and we are very fortunate that nobody was caught or carried in it. This avalanche fractured with the third skier on the slope at the skier's skis and ran full track through a convoluted avalanche path. Our group made several mistakes that we hope to learn from: 1. We did not complete a last minute check quick pit/ECT - we probably would have gotten a result that would have turned us back 2. We were path dependent - it was the end of a long day and this was the most direct skiable path back to our sleds 3. We were not familiar with the complete run - it wasn't a run we would have enjoyed much even without the avalanche and felt very unsafe in retrospect We were aware of the persistent slab problem (thank you Mark and Sarah) and discussed it at the beginning of the day then tested and looked through it during our tour - except on that final slope. That was a key mistake that could have had dire consequences for us. Please keep heads up out there and don't get lulled into a false sense of security because you aren't finding the problem everywhere - that's the sneaky part about persistent weak layers. - Solar aspects were warming throughout the day but it seemed that SE aspects specifically had the most WL activity by the end of the day - Observed no obvious signs of instability on non-solar aspects until unintentionally triggering a large persistent slab avalanche on a N aspect at 7100' (avalanches tab for more info)
Weather
- Air Temp
- 20
- Cloud Cover
- clear
- Wind Loading
- none
- Recent Snowfall
- 0
- Snow Avail For Transport
- small smounts
Snowpack
We dug a variety of hand pits to track subtle density changes in the upper snowpack throughout the day and found a variety of small wind affected pockets to avoid while climbing/skiing. We also dug a quick pit at 7350' on an East 31* slope (HS220cm) with an ECTN25 @ 195 stability test result on a subtle density change within the new snow. We did not observe facets above the early February crust in this pit and safely skied the slope. After triggering the persistent slab avalanche later in the day, a quick look at the crown revealed a 3cm layer of small grained facets above the early February crust buried ~55cm below the surface.
Avalanche
- Size
- D2.5 R4
- Type
- SS
- Count
- 2
- Aspect
- N
- Trigger
- AS
- Elevation
- 7100 ft
Our group had specifically decided not to ski southerly aspects today to avoid the rapid warming and potential avalanches expected. We observed one natural loose dry triggered storm slab on a steep SE slope at 11:22am that ran nearly full track. This slope caught morning light early and had been cooking for the entire morning beforehand and confirmed our avoidance of solar aspects. Our group unintentionally triggered a large persistent slab avalanche on a N aspect at 7100' near the end of the day and thankfully no one was caught or carried. The avalanche caught us completely off guard given our other observations throughout the day on similar aspects and at similar elevations. This avalanche fractured on facets above the early February crust and ran full track.