Rising temperatures coupled with spring sun can pack a punch and quickly initiate natural avalanche activity and weaken cornices. Be ready to back off slopes as the surface becomes moist. Moderate wind could help keep things cool, but could also be building new wind slabs.
Cornices are fragile due to rapid growth from recent snow and wind. Strong sun will further weaken them. Cornice falls are dangerous in their own right and they can also trigger slabs on slopes below.
Storm slabs are most likely to be reactive:
- at elevations with dry snow experiencing rapid warming for the first time (around 1800 m)
- on dry southerly aspects seeing strong sun for the first time
- in freshly wind loaded terrain features at upper elevations
Wet loose avalanches are possibly below treeline.
Dry loose avalanches will be very likely on steep south facing slopes at upper elevations when the sun comes out in the afternoon.
Tuesday night: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 500 m. Alpine temperature -7.
Wednesday: Sunny. Light to moderate southwest wind. Freezing level 2000 m. Alpine temperature -1.
Thursday: Mix of sun and cloud. Moderate southwest wind. Freezing level 2000 m. Alpine temperature -1.
Friday: Scattered flurries. Light to moderate southwest wind. Freezing level 1800 m. Alpine temperature -4.
On Monday, numerous skier and explosive triggered storm slab avalanches were reported size 1-1.5, largely on NW aspects. By Tuesday, storm slabs became more stubborn to explosives and results were limited. Observations in the Hellroaring area, which received less snow, include a few size 1 wind slabs and a cornice-triggered size 1.5.
Reports during the storm on Sunday include several natural storm slabs size 1-2 and a natural size 2 loose wet avalanche on a northeast aspect around 1700 m. It is suspected to have scrubbed down to a crust near the ground, as rain and warm temperatures destabilized the full depth of the snowpack. Keep this one in mind as the snowpack heats up again on Wednesday.
15-40 cm of recent snow has seen some redistribution by southwest to northwest wind, and seems to be bonding well with underlying surfaces. Dry snow that sees direct sun or experiences above freezing temperatures for the first time Wednesday may become reactive as it settles rapidly. Crusty surfaces below treeline will become moist with rising freezing levels.
A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and small surface hoar has been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers. Deeper layers are strong and have been unreactive over the past few weeks.
