Avalanche Forecast

Issued: Mar 19th, 2013 10:16AM

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

pmarshall, Avalanche Canada

Cariboos.

There is much uncertainty surrounding the March 10 Surface Hoar and how it will respond to Wednesdays storm. Hedge your bet and stick to simple terrain free of overhead hazard.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Synopsis: A low pressure system approaches from the SW which should deliver strong wind and significant precip. A trailing cold front in it’s wake will bring the freezing levels down to valley bottom on Thursday. Wednesday: Freezing Level: 1500m. Precipitation: 15 /20mm – 30/40cm Wind: Strong SWWednesday night: Precipitation: 10/15mm – 20 – 30cm.Thursday: Freezing Level: Valley Bottom. Precipitation: Isolated convective flurries. Wind: Moderate to strong NW.Friday: Freezing Level: Valley Bottom. Precipitation: Isolated convective flurries. Wind: Moderate NW.

Avalanche Summary

No new avalanche was reported Sunday. A natural avalanche cycle to size 2.5 took place in response to new snow loading on Saturday night.

Snowpack Summary

Generally moderate amounts of new snow fell on Saturday night and Sunday and have have been distributed by strong northerly winds into deeper windslabs in lee terrain. Depending on elevation, these recent accumulations may overlie a thick rain crust. Up to 1m below the surface is a layer surface hoar or a sun crust buried on March 10th. I expect another round of natural activity on this layer as the coming storm adds a significant new load on Wednesday. At lower elevations where last week's heavy rain saturated the snowpack, subsequent cooling has dramatically strengthened the snow.Weaknesses lower in the snowpack have become unlikely to trigger.Widespread cornice development has also taken place, and cornices are reported to be very large and weak.

Problems

Storm Slabs

Significant new snow combined with strong SW winds on Wednesday will begin to stack up on a variety of old surfaces including old storm/wind slabs and variable crusts below treeline. This will likely set the stage for a natural avalanche cycle.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Persistent Slabs

Around 1m of snow rests on the March 10 surface hoar/sun crust combo. This layer may roar back to life Wednesday as storm totals stack up which would result in a surprisingly large and destructive avalanche cycle.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>Stick to simple terrain with zero overhead hazard.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 7

Valid until: Mar 20th, 2013 2:00PM