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Avalanche Forecast

Archived

Mar 13th, 2021–Mar 15th, 2021

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

Regions

North Rockies.

The Sunday hazard is higher (3-3-3) in the north where 35+ cm of new snow has fell. Sunny & warm weather will destabilize the snowpack throughout the region with potential for very large avalanches during peak warming, cornice fall & large loose wet avalanches may be widespread.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

The heat is on until Sunday night, and then we get into a nice pattern of warm days and cooler nights.

SATURDAY NIGHT: Freezing level holding around 2000 m, strong to extreme southwest wind, no significant precipitation expected. 

SUNDAY: Scattered cloud cover, freezing level holding between 1500 & 2000 m, strong southwest wind, a bit of rain/snow possible late in the day. Freezing level returning to valley bottom Sunday night.

MONDAY: A few clouds, freezing level rising to 1600 m, moderate west/southwest wind, no significant precipitation expected.

TUESDAY: A few clouds, freezing level rising to 1800 m, moderate southwest wind, no significant precipitation expected.

Avalanche Summary

Our field team noted some loose wet avalanches to size 2 in their MIN while skiing near McBride on Friday. 

The rising freezing level this weekend may induce a natural avalanche cycle as the snow is destabilized by warming temperatures. Some natural cornice failure was noted on Thursday which is likely a portent of things to come. Our field team found some large and disturbingly wide avalanches in the Hasler Tuesday, lots of compelling images in their MIN report here. It's suspected that these are running on facets that are about 80 cm below the surface.

This adds to the tally of recent large avalanches they started collecting in Pine Pass on Monday. All of this activity leaves me feeling uneasy about a big warm up this weekend. 

Snowpack Summary

The northern portion of the region around the Pine Pass has picked up 35 new cm as of Saturday afternoon but very little new precipitation has fallen in the southern 2/3 of the region. This snow is expected to be redistributed by the strong southwest wind and will also feel the heat of the rising freezing levels this weekend.

The freezing level crept up to about 1850 m Friday leaving a sun crust on solar aspects. The freezing level is expected to be higher Saturday night and Sunday with plenty of sun poking through scattered cloud cover. This rise in temperature is going to be a good test for our snowpack. Wind effect is widespread in the alpine and treeline across the region.

About a metre of snow covers a weak layer of facets buried mid-February. Slightly deeper there is a widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.

Terrain and Travel

  • Avoid avalanche terrain during periods of strong sun.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.

Problems

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.

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.

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.