Avoid pushing into aggressive terrain while our snowpack adjusts to the massive load of new snow. Natural avalanches are likely to become increasingly scarce, but the potential for large human triggered avalanches remains very serious.
Large, dangerous wind slabs have formed as a result of recent snowfall and strong winds. Natural avalanche activity is expected to decrease, but human triggered avalanches remain likely. Newly formed wind slabs combined with deeply buried persistent weak layers makes the consequence of triggering any avalanche high.
Two surface hoar layers are found 50-100 cm and 90-140 cm below the surface. These layers continue to produce large natural and human triggered avalanches, particularly at shaded treeline elevations where the surface hoar is well preserved.
Friday night: Clear. Light to moderate east winds. Alpine high temperatures around -10.
Saturday: Mainly sunny. Light to moderate northeast winds. Alpine high temperatures around -10.
Sunday: Mainly sunny, becoming cloudy overnight. Light to moderate southwest winds, increasing over the day and overnight. Alpine high temperatures around -10.
Monday: Cloudy with flurries bringing about 5 cm of new snow by end of day, increasing overnight. Moderate to strong south winds, increasing overnight. Alpine high temperatures around -7.
15-25 cm of new snow over Thursday brought snow totals from the first week of March to about 100 cm or more. Each round of snowfall has been accompanied by strong south winds, forming reactive storm slabs and burying two layers of surface hoar from February increasingly deeply.
The first of these layers was buried on March 1st and is currently 50-100 cm below the surface, the other was buried on February 19th and is closer to 90-140 cm below the surface, with the greatest depths found at higher elevations. On solar aspects (south through west) this surface hoar may be resting on a buried crust which has acted as an excellent sliding surface for overlying slabs. Reduced accumulations of recent snow overlie a rain crust below about 1000 m. The most suspect slopes can be found at treeline elevations and at the higher end of below treeline where preserved surface hoar most likely exists.
A layer of weak and sugary faceted grains that formed in January may be found about 130 to 180 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers have produced a few very large natural and explosive triggered avalanches over the past two weeks.
A parade of storms over the past week has produced continuous cycles of large natural avalanches. These avalanches have failed on a mix of storm interfaces and persistent weak layers.
Several more size 1 to 2 (small and large) persistent slab avalanches were triggered with skier traffic in the Stewart area on Thursday, releasing in remarkably low angle terrain. Weather limited observations in the Terrace area, although one new size 2.5 storm slab was observed failing on a reloaded slope and increasing the debris in its runout zone.
On Wednesday natural storm and persistent slab avalanches to size 3 were reported from a variety of aspects below 1200 m. Activity was likely occurring at higher elevations too, but poor visibility limited observation.
Natural storm slab avalanches (size 2-2.5) were reported at higher elevations on Tuesday, and several size 1-2 human triggered slabs were reported on north facing treeline slopes. The human triggered slabs failed on the March 1st surface hoar layer. On Monday several natural size 2 avalanches were observed on open rollovers at treeline, also failing on the March 1st surface hoar.
There have also been some isolated reports of very large (size 2.5-2.5) natural and explosive triggered avalanches on deeper weak layers (including one that occurred on March 1 that failed on the January facet layer on a northeast slope at 1500 m near Kitimat and a few on March 2 that failed on basal facets on east and southeast alpine slopes near Ningunsaw).
Large cornice and glide crack failures continue to be reported as well.
