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Avalanche Forecast

Archived

Mar 7th, 2020–Mar 8th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Glacier.

The buried February 22 surface hoar layer (weak layer) is lurking at a depth within range of human triggering. Conservative use of terrain is advised.

Weather Forecast

Flurries today with accumulation around 8 cm. Alpine temperature a High -4 C with ridge wind southwest 10-30 km/h. The freezing level should rise to 1600m. A trace of snow overnight with cooling temperatures. Sunday-Monday expect a mix of sun and cloud, SW winds in the moderate range and ridgeline temperatures in the -10C--14C range.

Snowpack Summary

15cm+/- of storm snow with light winds covers recently formed windslabs in open terrain features at all elevations. Previous wind effect appears to be highly variable. Below these slabs, the Feb 22nd persistent weak layer is now buried down 50-80cm, and consists of 3-7mm surface hoar on all aspects up to 2450m, and a crust on solar aspects.

Avalanche Summary

Glacier National Park VS staff responded to a InReach call for a sled triggered size 2.5 slide that occurred inside the E boundary of Glacier National Park in the Bald Hills. Evidence indicated 2 sleds were involved and the group self extricated. Five natural avalanches to size 1.5 off Mt MacDonald east of the pass in the highway corridor.

Confidence

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.