Archived Avalanche Forecast - Purcells    

Date Issued   Monday, 02 February 2015 4:41 PM   	   	
Valid Until    Tuesday, 03 February 2015 10:00 PM

A new storm slab is developing. Watch for continued loading from the forecast new snow and wind this 
week.

Public Avalanche Forecast

Danger Rating: 

Tuesday :

Alpine: 2 - Moderate Heightened avalanche conditions on specific terrain features. Evaluate snow and 
            terrain carefully; identify features of concern.
Treeline: 2 - Moderate Heightened avalanche conditions on specific terrain features. Evaluate snow 
              and terrain carefully; identify features of concern.
Below Treeline: 1 - Low Generally safe avalanche conditions. Watch for unstable snow on isolated 
                    terrain features.

	                Wednesday 	    Thursday
Alpine 	            2 - Moderate 	3 - Considerable
Treeline 	        2 - Moderate 	2 - Moderate
Below Treeline 	    1 - Low 	    2 - Moderate

Confidence: Fair - Timing, track, or intensity of incoming weather system is uncertain

Problem: Persistent Slabs

A layer of surface hoar buried in the upper meter of the snowpack has been the failure layer for 
recent natural and human triggered avalanches. Storm slab avalanches in motion may step down to the 
buried weak layer.

Travel and Terrain Advice: Choose well supported terrain without convexities.

What Elevation Zone? - Alpine, Treeline
Which Slopes? - All
Chance of Avalanches? - Possible
Expected Size? - Large


Problem: Storm Slabs

A new storm slab is developing above a crust and/or surface hoar that was buried in the past few 
days.

Travel and Terrain Advice: Be cautious of sluffing in steep terrain. Be aware of party members below 
you that may be exposed to your sluffs.

What Elevation Zone? - All
Which Slopes? - All
Chance of Avalanches? - Likely
Expected Size? - Small

Problem: Deep Persistent Slabs

Deeply buried weak layers may react to large loads like an avalanche in motion, or could be triggered 
by light loads in thin and variable snowpack areas.

Travel and Terrain Advice: Stay clear of thin areas that may propagate to deeper instabilities. Pay 
attention to overhead hazards like cornices.

What Elevation Zone? - Alpine, Treeline
Which Slopes? - All
Chance of Avalanches? - Unlikely
Expected Size? - Large, Very Large

    Forecast Details

Avalanche Summary

No new avalanches reported. I suspect that the new storm snow may not bond well to the old crust 
and/or surface hoar, resulting in easy triggering of a thin soft slab.

Snowpack Summary

A thin layer of new storm snow has fallen on a variety of old surfaces, including hard crusts, 
breakable crusts at higher elevations, and surface hoar in some areas. A melt freeze crust can be 
found up to about 2200m. At higher elevations, the surface is heavily wind affected. The depth of 
the mid-January surface hoar is highly variable across the region and it may have been destroyed by 
warmth at low elevations. Where it does exist, it can be found between 30 and 70 cm below the 
surface. The mid-December surface hoar layer lies below a strong mid-pack down about 60 to 120cm. 
Both of these persistent layers have been reactive recently. The mid-November weak layer of crusts 
and facets can still be found near the bottom of the snowpack. It has been unreactive lately, but 
should be on your radar in shallow snowpack areas where there is more chance of triggering.

Weather Forecast

Flurries overnight are expected to bring 2-3 cm by Tuesday morning. Tuesday and Wednesday should be 
mostly dry with a chance of light flurries. The next storm should start early Thursday morning and 
at this time looks like it could bring 5-10 cm by Friday morning.