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Avalanche Forecast

Archived

Feb 23rd, 2020–Feb 24th, 2020

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 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

South Rockies.

This forecast is based on 5 to 10 cm Sunday night and another 5 to 10 Monday, but some valleys could see more. The new snow is coming to rest on a variety of potential weak layers that may allow for surprisingly touchy storm slabs. Time for conservative terrain choices.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

There’s quite a bit of uncertainty surrounding the precipitation associated with Monday’s highly variable storm. The forecast really mellows out for the rest of the forecast period though.

SUNDAY NIGHT: Freezing level around 1500 m, light to moderate west/northwest, 5 to 10 cm of snow.

MONDAY: Overcast at dawn with some clearing in the early evening, freezing level around 1000 m, light variable wind, 5 to 10 cm expected with potential for some enhanced convective snowfall producing as much as 20 cm throughout the day.

TUESDAY: Scattered cloud cover, freezing level starting at valley bottom rising to about 1500 m, light southwest wind at lower elevations, moderate to strong west/northwest wind at ridge top, no significant snowfall expected.

WEDNESDAY: Scattered cloud cover, freezing level starting at valley bottom rising to about 1500 m, light southwest wind at lower elevations, moderate to strong northwest wind at ridge top, no significant snowfall expected.

Avalanche Summary

No notable avalanche activity was reported in the region since Tuesday, some storm slab avalanche activity is expected Sunday Night into Monday

The most recent deep persistent slab activity we know about is described in this MIN report from February 11 and this MIN report on February 9th. This layer may become reactive again with a large trigger (like a cornice failure) or a sharp change in weather. 

Snowpack Summary

Sunday/Monday's storm snow is covering a variety of old surfaces including a firm crust on solar aspects, soft faceted snow and possibly surface hoar in sheltered areas, and old wind slabs near ridge crest.

A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. 

A well consolidated and settled mid-pack overlies generally weak basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.