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Archived

Avalanche Forecast

Mar 19th, 2013–Mar 20th, 2013
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: 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.

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.

Avalanche 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