Wednesday April 3, 2019
Cornice Fall, Loose Wet, Wind Slab
Travel & Terrain Advice
Assess where the snow/rain elevation change is and adjust for what type of avalanches one can expect as you ascend.
Avoid large open slopes and exposure above terrain traps as rain saturates the snow pack at lower elevations.
Avoid lee (wind loaded) slopes at upper elevations where snow falls vs rain.
Give cornices a wide berth (both above and especially on slopes below) as rain will increase the potential for them to fail and fall.
Not an avalanche concern, but in general…. Watch out below treeline as the snow pack is getting thinner. Be wary of creeks/holes opening up and rocks becoming exposed.
No new avalanches have been reported in the past three days, beyond minor human triggered loose wet sloughs up to size one on steep treeline solar slopes in the warm afternoons.
High freezing levels, and rain falling higher in the hills for the first time this season will result in weakened cornices. It is possible that cornices will fail naturally or with human triggers in the alpine and at treeline when the rain saturates them. If these fail we may see avalanches up to size two to three on NW to NE aspects.
Unfortunately we can expect rain to fall on the snow at below treeline and treeline elevation bands. This rain will very likely result in loose wet avalanche activity up to size one to two. These wet slides will be easily triggered by human activity, may possible even fail naturally and will be widespread on all aspects.
Snow in significant quantities will fall at upper elevations (in the alpine and treeline) on Wednesday and Friday. During the next three days moderate winds will transport this new snow to lee NW to NE slopes and create the potential for wind slab avalanches up to size two. Landing on the exposed crust from the past week, these slabs will likely be triggered by human activity and may possibly trigger naturally.
Spring conditions have dominated the past week with clear cold nights creating a thick crust and warm sunny days seeing the surface of solar slopes going moist down to 4 cm. A weak layer mid snow pack (facets above a crust) has produced moderate results in pit tests but seams well bridged by snow above and is insensitive to triggering.
|Surface||4-15 cm crust|
|Upper||moist well settled snow|
|Mid||mainly settled snow with a weak layer above a crust (down around 60 cm)|
No new snow has fallen in the past week and the area has been dominated by a typical spring pattern, cold and clear at night (just below 0 degrees) and warm (up to +11) and sunny during the day. The goggle tans have been coming along nicely!
Fluctuating freezing levels are the story over the next three days… Where (what elevation) will the rain switch to snow? Weather models have the mixed precip line bouncing between 1000 m and 1300 m.
Wednesday - 9 to 14 mm of precip (*note 1 mm of precip falling as snow is typically equal to 1 cm of snow accumulation), temps 0 to 4 degrees, winds moderate SE to SW, freezing levels 1500 to 1800 m.
Thursday - 2 mm of precip, temps -2 to 1 degree, winds moderate SE, freezing levels 1100 to 1300 m.
Friday - 5 to 18 mm of precip, temps -2 to 2 degrees, winds moderate SE, freezing levels 1100 to 1500 m.
Posted on Wednesday April 3, 2019 by Bill Phipps