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Avalanche Forecast

Archived

Mar 23rd, 2021–Mar 24th, 2021

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

Regions

South Columbia.

Look for cold dry snow on north facing terrain at upper elevations. Be wary as this may also be where wind slabs develop.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

TUESDAY NIGHT: Flurries and snow, 10-15 cm by morning and rain at lower elevations. Moderate southwest wind increasing though the night, alpine low -12C, and freezing level hovering around 1000 m.

WEDNESDAY: Ongoing flurries, accumulating 15-20 cm by the end of day. Moderate southwest wind decreasing though the day, alpine high 0C, and rising above 1500 m.

THURSDAY: Unsettled with isolated flurries and sunny breaks. Light west wind, alpine high -1C, and freezing level above 1600 m.

FRIDAY: Unsettled flurries, little accumulation. Moderate northwest wind, alpine high +2C, and freezing level rising above 1800 m.

Avalanche Summary

On Monday, a few natural storm slab avalanches to size 2 were observed in the alpine, likely failing overnight and numerous loose dry avalanches to size 2 were reported as well. Skiers triggered size 1-1.5 storm slab avalanches 20-50 cm deep on south and east aspects above 2000m, and a couple of cross-loaded convexities in open treeline. Explosives triggered several size 1-1.5 avalanches on NW-N-NE aspects above 1800 m. A large (size 2) natural cornice failure occurred overnight, entraining the storm snow but not pulling a slab below. And several natural storm slab avalanches size 2-2.5 were reported in Glacier NP, occurring on north-northwesterly aspects above 1950m.

On Sunday, explosives and skier traffic triggered numerous size 1 avalanches, new and touchy cornices were observed. A few small dry loose avalanches and sluffing in steep terrain was also reported.

On Saturday, explosives triggered small (size 1-1.5) storm slabs from north-northeast aspects above 2000 m. A skier also triggered a small (size 1) wind slab on a steep convex roll on an easterly aspect at treeline. Sluffing was reported in steep terrain. In Glacier NP, a handful of storm slabs size 1.5-2.5 released naturally from steep north-northwest aspects above 2000m.

On Friday, several glide slab avalanches (size 2-3) were observed on south and east aspects around the TCH highway corridor. Loose wet avalanches up to size 2.5 were reported around the region; a natural loose-wet cycle was reported around Rogers Pass initiating with evening rainfall.

Snowpack Summary

Southwesterly winds and flurries will form fresh slabs in lee features. 20-40 cm (up to 60 cm in areas) recent snow covers dry and compacted snow on polar surfaces above 1800 m and crusts on solar slopes; storm snow has been sluffing easily on the crust. In some areas of the region, surface hoar (4-10 mm) has been reported below the recent storm snow in shaded north-facing slopes at upper treeline and above. Large cornices loom over alpine ridgetops. Spring temperatures and sun are producing a melt-freeze snowpack below 1500 m and higher on solar slopes.

Persistent weak layers of surface hoar, crusts, and/or facets 80-120 cm down have recently been unreactive and no recent avalanches have been reported on these layers. 

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Carefully evaluate steep lines for wind slabs.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.