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Avalanche Forecast

Archived

Mar 30th, 2017–Mar 31st, 2017

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

Regions

Purcells.

Warming and solar induced avalanches are likely. Smaller wind slabs, storm slabs or cornice fall could "step down" and release persistent weak layers resulting in large avalanches.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Friday

Weather Forecast

Drier, sunny conditions expected on Friday and then back to unsettled weather with a mix of sun, cloud and warming for the weekend.Friday: Mix of sun and cloud. Alpine temperatures near -2 and freezing levels 2000 m. Ridgetop winds light from the South.Saturday: Trace of new snow. Alpine temperatures near -5 and freezing levels 1800 m. Ridgetop winds moderate -strong from the West.Sunday: Mix of sun and cloud with isolated flurries up to 5 cm. Alpine temperatures near -7 and freezing levels 1300 m. Ridgetop winds light with strong gusts from the West.

Avalanche Summary

On Wednesday, a couple of larger storm slab avalanches were reported. They were explosive controlled size 2 and size 3 from South aspects 1800 m and above. There was also one skier controlled size 1.5 slab avalanche that failed on a crust from a South aspect around 2200 m. On Friday natural avalanche activity may occur and rider triggering is likely, especially with the strong influence of solar radiation, warming and wind. Fragile cornices are also suspect, they are large enough and act as heavy triggers for deeper slab avalanches to release on the slopes below. If you're traveling below treeline where the avalanche hazard is lower than it is in the alpine you should remain diligent with your terrain use, mitigate overhead hazards by avoiding or lingering in run-out zones where large avalanches could come down from above. Check out the recent Forecasters' Blog here

Snowpack Summary

10-30 cm of recent snow has fallen at upper elevations and caps a sun crust on solar aspects. This brings 40-60 cm of accumulated snow over the past week. This recent snow overlies a widespread crust below 2300 m and higher on solar aspects. Alpine wind has recently been strong mainly from the SW and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices also exist along ridgelines. At higher elevations, the February crust/facet layer is now down around 130-150 cm and has been reactive with several avalanches recently releasing on it. It is expected to be most reactive in the alpine where the snowpack remains dry. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have stepped down to these layers recently resulting in very large avalanches. These layers remain a concern during this stormy period ending with warmer temperatures and sunshine. The snowpack does not adjust well to change, and these deeper weak layers should remain on your radar through the forecast period.

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.

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.

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.