Avalanche Forecast

Archived

Apr 11th, 2023–Apr 12th, 2023

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Jasper, Brazeau, Churchill, Cirrus-Wilson, Fryatt, Icefields, Maligne, Marmot, Miette Lake, Pyramid.

Continued uncertainty regarding forecasted precipitation amounts. Convective flurries could produce up to 20cm overnight Tuesday into Wednesday. Moderate southwest winds on Tuesday have added to the new wind slab which has shown the ability for wide propagation in the alpine.

Rolling closures planned for Maligne Lake Road south of Medicine Lake 1500-1700hrs for avalanche control.

Confidence

Moderate

Avalanche Summary

Explosive control Sunday on a large road side cut bank at 1800m produced several wet loose avalanches up to size 2.5 - isothermal running on the basal facets.

Patrol on 93 Monday and Tuesday observed 3 size 2 wind slabs variable aspects in the alpine showing descent propagation and one size 2.5 off Saskatchewan that reached the run out - limited visibility on Tuesday.

Don't forget to post avalanche observations to the MIN.

Snowpack Summary

Up to 20cm (14mm) precipitation since Sunday sits atop our April 9 melt freeze/solar crust. Snow in the alpine was accompanied by strong southwest winds creating new wind slab lee and cross loaded features. Snowpack below 1800m is in a diurnal isothermal freeze thaw. The mid pack above this elevation consists of multiple layers of dense wind effected snow in open areas, sun crusts on solar aspects, and facets. Depth hoar and basal facets make up the base of the snowpack.

Weather Summary

Continued unsettled conditions are expected Wednesday. Models once again vary showing trace to 15cm possible. Winds will be moderate to strong SW overnight falling to light values by Wednesday morning. Freezing level 1500m Wednesday and Thursday; valley bottom overnight. Clearing trend Thursday.

Terrain and Travel Advice

Minimize exposure during periods of heavy loading from new snow, wind or rain.
If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.