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Avalanche Forecast

Archived

Feb 24th, 2020–Feb 25th, 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

South Rockies.

The region picked up 10 to 35 cm from the recent storm which could translate into surprisingly deep slabs, especially in wind exposed features near ridge crest. Tuesday is not the day for bold travel plans, keep it mellow as the snowpack adjusts to the new snow

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

The forecast is marked by a nice diurnal temperature swing with the freezing level rising progressively higher each day and then returning to valley bottom at night which is all well and good. Things change Friday night when the freezing level is expected to go to 2500 m (ish). Get the cold snow while you can.

MONDAY NIGHT: Freezing level at valley bottom, light variable wind, trace of snow possible.

TUESDAY: 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 precipitation expected.

WEDNESDAY: Broken 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 precipitation expected.

THURSDAY: Clear skies, freezing level starting at valley bottom rising to about 2000 m, light to moderate west wind at lower elevations, strong northwest wind at ridge top, no precipitation expected.

Avalanche Summary

We're short on post storm observations, but control work produced storm slabs to size 1.5 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

The Sunday/Monday storm produced 10 to 35 cm of storm snow which now rests on a variety of old surfaces including a firm crust on solar aspects, soft faceted snow and surface hoar in sheltered areas, and old wind slabs near ridge crest. The new snow has been formed into variable wind slabs in exposed terrain features, especially those near ridge crest.

A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17.

The mid-pack is well settled and strong, but the base of the snowpack contains 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.