Very large natural and human triggered avalanches continue to be reported, and some natural activity may persist into Friday. Only the simplest avalanche terrain free of overhead hazard is appropriate while the snowpack adjusts to the most recent load.
Two surface hoar layers are found 30-60 cm and 75-125 cm below the surface. These layers continue to produce large natural and human triggered avalanches, particularly at treeline elevations where the surface hoar is well preserved.
Large dangerous storm slabs have formed. As snowfall tapers off Thursday night natural avalanche activity is expected to decrease, but human triggered avalanches are very likely. Fresh storm slabs combined with several persistent slabs makes the consequence of triggering any avalanche high.
One last pulse Thursday night, and then we’re into a clearing trend for the weekend.
THURSDAY NIGHT: Freezing level at valley bottom, moderate southwest wind, 4 to 8 cm of snow.
FRIDAY: Scattered cloud cover, freezing level rising to about 600 m, light south wind, no significant precipitation expected.
SATURDAY: Clear skies, freezing level rising to about 700 m, light east wind, no significant precipitation expected.
SUNDAY: Clear skies in the morning building to overcast before sunset, freezing level rising to about 600 m, light wind initially with increasing wind out of the west/southwest throughout the day, no significant precipitation expected.
A steady pulse of storms over the past week has produced numerous cycles of large natural avalanches. These avalanches have failed on a mix of storm interfaces and persistent weak layers. Similar activity can be expected on Friday.
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. On Friday and Saturday there were reports of natural and skier triggered size 2-3 avalanches failing on the February 19th surface hoar layer, primarily on north and east facing slopes around treeline.
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 too.
15 to 35 cm of snow fell Wednesday night into Thursday with strong south/southeast wind. We're expecting another 10 to 25+ cm Thursday afternoon/evening. Fresh storm slabs have almost certainly formed.
Recent storms have buried two layers of surface hoar that continue to be reactive and produce large avalanches. One layer was buried on March 1st and is currently 30-80 cm below the surface, the other was buried on February 19th and is currently 75-125 cm below the surface. On solar aspects (south through west) surface hoar may be resting on a buried crust which could be a very problematic setup. A rain crust exists below 1000 m. Be very suspect of slopes 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 120 to 170 cm deep, and an early-season melt-freeze crust linger at the base of the snowpack. These layers have produced a few very large natural and explosive triggered avalanches over the past two weeks.
