Avalanche Forecast

Issued: Mar 19th, 2015 9:18AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Persistent Slabs and Loose Wet.

swerner, Avalanche Canada

Cariboos.

Snow, rain and wind combined with buried weak layers make the perfect recipe for avalanches. The upper snowpack is complex, keep it simple and use a very conservative approach to terrain selection.

Summary

Confidence

Good

Weather Forecast

A series of pacific frontal systems will bring waves of precipitation to the Interior Ranges over the forecast period. Friday will see overcast skies, precipitation amounts 5-15 mm, ridgetop winds moderate from the SW and freezing levels 1700-2000 m. Continued precipitation on Saturday with amount up to 15 mm , ridgetop winds light-moderate from the SW and freezing levels near 1800 m. Later Saturday the front will start to move east setting up a clearer, drying trend for Sunday. Freezing levels will initially drop to valley bottom overnight Saturday then rise steadily during the day with treeline temperatures near 0 degrees.

Avalanche Summary

On Wednesday, natural and skier triggered slab avalanches were reported up to size 2. Both avalanches were reportedly over steeper convex terrain features on northerly aspects above 2100 m. Widespread natural avalanche activity is expected through the weekend due to new snow, rain and strong SW winds. Avalanches failing on the the mid-February persistent interface will likely have wide propagations and be large and destructive.

Snowpack Summary

At higher elevations, new storm snow up to 20 cm sits over a plethora of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs. This gives us anywhere from 40-80 cm over the mid-February persistent weak interface. This interface has recently been very reactive and I don't suspect that to change during this stormy period. Strong winds have redistributed new snow into wind slabs on leeward terrain features. Lower elevations up to treeline are sporting spring-like, melt-freeze conditions. The late-January crust/surface hoar layer (over 1m deep) and the mid-January surface hoar (around 1.5m deep) have been dormant for several weeks.

Problems

Storm Slabs

Touchy storm slabs continue to build and sit over a weakness from mid-February. These will likely be reactive naturally and by human-triggers through the weekend.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

A persistent weak interface buried mid- February 30-60 cm below the surface is responsible for numerous large slab avalanches.

Be aware of the potential for wide propagations.>Remote triggering is a concern, watch out for adjacent slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Loose Wet

Steady rain and warming at lower elevations will saturate and weaken the upper snowpack.

Watch for clues of instability, like natural avalanche activity, sluffing off of cliffs, and snowballing. >Avoid exposure to terrain traps where the consequences of a small, wet avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Very Likely

Expected Size

1 - 3

Valid until: Mar 20th, 2015 2:00PM