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Avalanche Forecast

Archived

Nov 22nd, 2019–Nov 23rd, 2019

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

Regions

Purcells.

If storm totals surprise us and exceed 15 cm Saturday then alpine hazard will be considerable. The region has a weak and highly variable snowpack right now, it may not take much to produce natural persistent slab avalanches, especially if storm totals approach 25 cm.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

It’s late November and it looks like we’re entering a more winter-like pattern this weekend. The Purcells (especially the northern section) should get a nice re-fresh from the system.

FRIDAY NIGHT: Trace of snow possible, freezing level near valley bottom.

SATURDAY: Overcast, freezing level around 1000 m, moderate west/southwest wind, 1 to 10 cm of snow possible, with another 2 to 6 cm possible Saturday night.

SUNDAY: Broken cloud cover, freezing level around 1000 m, light to moderate northwest wind, 1 to 5 cm of snow possible.

MONDAY: Broken cloud cover initially with some clearing to scattered in the afternoon, freezing level around 500 m, light northwest breeze, 1 to 5 cm of snow possible.

Avalanche Summary

On Thursday In the central portion of the region a natural size 2 persistent slab avalanche was observed on a north/northeast facing slope at 2300 m. This could be a portent of things to come this weekend, especially if storm snow totals exceed 20 or so centimeters.

Snowpack Summary

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.