Thursday March 14, 2019
Cornice Fall, Loose Wet, Persistent Slab, Wind Slab
Travel & Terrain Advice
On Thursday, be cautious of travel in Leeward terrain (downwind areas). On Friday, rain and warming will further increase avalanche hazard, Simple Terrain below 30 degrees will be the best option this weekend.
Avalanche professionals have reported initiating size 1 avalanches through avalanche control methods. Leeward unsupported terrain in the Jutland Peak area also had reports of size 1 and size 2 natural avalanches during Monday’s Extreme wind and precipitation event.
New snow, extreme winds, near mountain top freezing levels are all factors that will exacerbate cornice development and subsequent cornice failure due to loading. Be very cautious in terms of your route selection this weekend and do not travel below slopes with overhead exposure from cornices.
On Friday, the temperature is set to rise to above zero in the Alpine. This general increase in temperature, coupled with precipitation (likely rain for Friday) will add increased stress to newly fallen snow and potential wind slabs from Thursday’s Extreme wind events. Slopes steeper than 30 degrees that receive rainfall will become likely areas to trigger avalanches.
There are several reactive persistent weak layers in the upper 60cm of the Vancouver Island snowpack. These issues will become increasingly more hazardous with forecasted wind loading (Thursday), rain loading (Friday) and the general warming air temperatures this weekend. Be extremely vigilant as these layers remain a main concern despite no new reports of human triggered avalanches. As temperatures rise, expect the likelihood of triggering to increase for these layers.
Extreme to Strong Winds are forecast for the next several days from the south. Expect Northerly (lee) aspects to provide good areas for triggering avalanches as precipitation in the form of rain and snow will cause an increasing hazard in avalanche terrain.
The snowpack on Vancouver Island is a snow geek paradise however it contains a number of reactive persistent weak layers (PWL). These PWL’s, coupled with extreme winds and near mountain top freezing levels all lead to an exacerbation of the snowpack as we begin the shift from winter into a spring diurnal (melt freeze phase).
Thursday we will see nearly 10cm of new snow and 70km/h winds, this will lead to wind slab hazards in leeward terrain. On Friday, we will see additional 5mm of precipitation but this may come in the form of rain which will additionally load fresh wind slabs and potentially further strain the deeper PWL problems within the upper 60cm of the snowpack.
|Surface||30-60cm of light dry powder snow, Friday freezing level and rain may alter snowpack surface|
|Upper||several reactive persistent weak layers, expect reactivity to increase with Friday warming and rain|
Cool temperatures and progressively increasing day time highs trend toward 0 degrees at Treeline during the day.
If forecast models are accurate, the new snow and extreme winds will progressively increase the avalanche hazard over the course of Thursday March 14th.
Thursday - 10 cm of new snow, Extreme winds from the South, temps -5 to -1 , freezing level 1,100M.
Friday- 1 to 5 mm of rain, Strong winds from S, temps -2 to +3, freezing level 1,800 M.
Saturday - trace to 1cm of new snow, strong winds from SE, . temps -1 to +2, Freezing level 1,300 M
Posted on Thursday March 14, 2019 by Ryan Shelly