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Archived

Avalanche Forecast

Jan 20th, 2020–Jan 21st, 2020
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: South Rockies.

Freezing levels are forecast to hover around 1400 m for the next couple of days before spiking into the alpine on Thursday. Until then, windslabs remain the main concern at upper elevations.

Confidence

Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast. Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday night: Clear. Moderate southwest winds. Alpine low -7 C. Freezing levels dropping to valley bottom.

Tuesday: Mostly cloudy with isolated flurries bringing a trace of new snow. Moderate southwest winds. Alpine high -4 C. Freezing level around 1400 m.

Wednesday: Broken cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high -3 C. Freezing level around 1400 m.

Thursday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds, becoming strong at ridgetop. Alpine high 0 C. Freezing level around 1800 m.

Avalanche Summary

On Monday we received reports of natural and explosive triggered windslab avalanches size 1.5-2.

On Thursday a natural size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here. 

Snowpack Summary

A crust can be found on solar aspects at lower elevations due to daytime warming on Monday. Recent snow has been loaded into pockets of soft windslab in alpine lees, and is settling in the mild alpine temperatures. At lower elevations it may remain unconsolidated. It sits over widespread windslab in exposed areas at all elevations.

A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. There is potential for this deep persistent layer to reawaken in the warm alpine temperatures later in the week.

Terrain and Travel

  • In times of uncertainty conservative terrain choices are our best defense.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Avalanche Problems

Wind Slabs

Strong westerly winds have blown recent snow into windslabs in lee features at alpine and treeline.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Deep Persistent Slabs

As temperatures trend warmer and freezing levels rise, there is potential for the deep basal weak layers to become active. Deep persistent slab avalanches on these layers are most likely to be triggered from shallow snowpack areas near rocky outcroppings.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 3