Wednesday December 26, 2018
Wind Slab, Loose Wet, Cornice Fall
Travel & Terrain Advice
Santa delivers a late Christmas present with some nice snow falling overnight on the 25th. But be wary…….
Avoid wind loaded lee (NE-NW) alpine slopes, open lee slopes at treeline and crossloaded features during and after the storm Christmas night (Tues Dec 25).
Continue to give cornices a wide berth both after Tuesdays storm and as temps and freezing levels rise late Friday (esp if there is rainfall).
As temps climb and if rain falls on our snowpack late Friday, avoid exposure above terrain traps (rocks, creeks, cliffs, depressions, gullies, etc) as loose wet slides tend to have significant strength, weight and power.
New avalanche activity limited to some loose dry surface snow sloughing on steep treeline cool shaded terrain (NW-NE).
New snow falling overnight Tuesday into early Wednesday will arrive with strong winds from the SE. These winds will transport snow to lee NW-NE slopes and to crossloaded features, creating wind slabs. These wind slabs will likely/possibly trigger with human loads and possibly trigger naturally from size 1-2. These will mainly be a concern in the alpine and open exposed (alpine like) treeline zones.
If rain arrives late Friday night, loose wet avalanche activity (esp from steep rocky shallow terrain) is a high possibility. Weather models are varied as to what elevations, how much and if rain will fall. If rain does fall at any elevation then wet loose avalanches are likely and could range in size from 1-2 on all aspects. Human and natural triggering during this potential rain event is likely. If we get lucky and this precipitation comes as snow at certain elevation bands, then change your mind set to storm slab avalanche problems.
Increased loading from either more snowfall, snow transport from high winds or rain will put more stress on the cornices that have built up recently on our alpine and open exposed treeline ridges. All three stresses are a distinct possibility over this coming forecast period. Pay attention to what weather factors truly do come into play over the next three days. It is always a good idea to give any cornice a wide berth from above a below. With the potential weather these cornice will have a higher (possible to likely) chance of triggering both naturally and with human loading. If they do release we can expect avalanches up to size 2.5 on NW-NE aspects (alpine and open exposed treeline).
Warm daytime temps and cool nights have begun to tighten/stabilize our multi layered snowpack.
|Surface||Alpine characterized by wind effected snow. Treeline and below, there is still some nice new snow preserved on northern aspects. However, on solar aspects the surface snow is now moist and heavier.|
|Upper||A supportive and tightening layer of recent snowfall, with the Dec 23rd storm shear gaining stability and becoming less of a concern.|
|Mid||The Dec 22nd crust is thin and well buried at treeline and alpine elevations, but it is thicker and can still be felt in the shallower snow below treeline.|
0 to 8 cm of new snow fell mid Monday Dec 24th with mild temps and light winds. Cold overnight temps Monday Dec 24th into Tuesday Dec 25th (Christmas) then tightened and helped stabilize our snowpack.
A moderate storm snow event late Tuesday (Christmas) night into Wednesday morning will bring snow with heavy SE winds. A lull Thursday is then followed by a significant warm up starting late Friday with potential rain to all elevations (freezing levels above 2000 m)
Wednesday Dec 26th - 10-25 cm of new snow with the largest amount forecast for the east (Strathcona) region. Winds strong (up to 60 km/h) from the SE. Temps ranging from -1 to -5. Freezing levels near 800 to 950 m.
Thursday Dec 27th - a trace to 4 cm of new snow. Winds variable and light rising to moderate SW by days end. Temps ranging from -1 to -4. Freezing level 800 to 950 m.
Friday Dec 28th - 1 to 5 cm of new snow potentially switching to rain late in the day/overnight at all elevations (weather models in debate as to how high the rain will go and in what quantity). Winds light SW rising to moderate. Temps -2 rising sharply later on up to +2. Freezing levels 700 rising to 2400 m. Nasty!
Posted on Wednesday December 26, 2018 by Bill Phipps