Avalanche danger will rise through the day as new snow and wind form fresh, reactive slabs. If you see more than 25 cm of new snow, treat avalanche danger as HIGH.
Potential exists for storm slab avalanches to step down to buried weak layers, resulting in very large avalanches.
A persistent slab problem formed by a crust down 70-130 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
New snow and wind are forming fresh, reactive storm slabs. New and recent snow may overlie a weak interface which could result in deeper and touchier than expected storm slabs.
A storm arriving overnight Thursday will deliver the bulk of snowfall over the day Friday. Areas in the west of the region such as Summer Lake are forecast to receive enhanced snowfall amounts, accumulating in excess of 50 cm by Saturday morning.
Thursday night: Snowfall 5-10 cm. Moderate to strong SW wind. Treeline temperature around -12 °C.
Friday: Snowfall 5-10 cm in most areas, upwards of 30 cm in the west of the region. Strong SW ridgetop wind. Treeline high around -4 °C.
Saturday: Snowfall tapering 3-6 cm. Moderate SW wind. Treeline high around -8 °C.
Sunday: Sunny. Moderate SW wind switching NW. Treeline high around -4 °C.
On Wednesday, explosive control work on North and South aspects in the alpine produced numerous loose dry and thin wind slab avalanches which started small but entrained mass in tracks, growing to size 2.5 and running up to 1300m. It is worthy to note that no deep slabs were triggered.
On Monday and Tuesday, natural, explosive and skier triggered storm slabs and loose dry avalanches size 1-2 were observed out of NE-SE aspects in the alpine.
The persistent slab problem has produced sporadic and spotty activity in the South Rockies and nearby regions. The most recent avalanche in the region was last Friday, when explosives triggered a size 2.5 wind slab avalanche that stepped down to the persistent slab layer on a SE aspect near treeline. Otherwise, persistent slab activity has not been observed in the region since before Christmas. A few recent notables from surrounding regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.
10-20 cm of new snow is forecast to fall by the end of Friday. Strong ridgetop winds will likely load new snow into leeward terrain features in the alpine. An accumulated total of 30-45 cm of new and recent snow now sits over a hard, faceted snow surface from the recent cold conditions, which may make for a weak bond at this interface.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now typically down 70-130 cm. The most recent avalanche on this layer was a week ago but sporadic activity has been observed in neighboring regions in the past week. This layer has created a tricky low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
