Note - This region has an "advisory" in the form of a blog which appears to be updated weekly or so.
It is managed by the Canadian Avalanche Association and is official, but it is presumably infrequent
and less detailed due to the remoteness of the region and limited information compared to their other
regional bulletins.

Archived North Rockies Report – February 19, 2015

Overview

Avalanche danger has been dropping since the re-freeze occurred over the weekend. Avalanche danger 
is expected to trend slightly lower or stay the same until the next storm system arrives.

Avalanche Activity

Some small loose moist avalanches were reported from the Murray range on the 15th that were visible 
from the Pine Pass area. In the Tumbler Ridge area this past weekend, natural cornice falls and slab 
avalanches up to size 3.0 were reported on solar aspects. I suspect that some loose moist avalanches 
continue to release on steep solar exposed aspects due to the sun and mild temperatures. Older slab 
avalanches up to size 3.0 that released during the warm weather last week were observed on all 
aspects in the alpine, and probably released on deeply buried facets.

Snowpack

The combination of sunshine and warmer air trapped in the alpine may allow for new surface crust 
formation at all elevations on solar aspects. Previously there was rain up to about 2500 metres near 
Tumbler Ridge, resulting in rain runnels on the surface and a breakable crust in the alpine. After 
the warming last week, the re-freeze has developed a substantial crust at treeline and below. This 
crust continues to develop through a diurnal melt-freeze process. Snow profile tests showed a weak 
layer of facets that were down just over a metre, failed with hard forces applied (the height of 
snow in this test location was 150 cm and the elevation was 1500 metres).

Weather Forecast

Cloud that developed on Thursday is expected to be replaced by mostly sunny conditions on Friday as 
the high pressure ridge re-builds on the coast. Saturday is forecast to be a mix of valley cloud and 
clear skies at higher elevations. A temperature inversion is expected to develop, trapping warmer 
air (still below freezing) in the alpine. The weak northwest flow that is forecast for Friday and 
Saturday may be replaced by a moderate southwest flow on Sunday as the ridge tilts and becomes a 
cut-off high. Starting Friday, there is no precipitation forecast until at least Thursday. Expect 
a mix of sun and cloud during the first half of the week. Overnight freezing should be down to valley 
bottoms.

Avalanche Problems

Deep Persistent Slab

The deeply buried layer of facetted crystals and the layer of basal facets continue to be a concern 
for deep releases resulting in large avalanches. This is a low probability/high consequence problem. 
Deep weak layers are more likely to be triggered during periods of prolonged warming, but may be 
triggered from shallow weak areas adjacent to large slopes.

Loose Wet

Loose wet avalanches may continue to release from steep terrain features on solar aspects.

Travel Advice

Watch out for loose wet snow falling out of steep terrain features that might scour moist snow from 
the slopes below. Avoid run-out zones from alpine solar aspects. Avoid thin snowpack areas adjacent 
to alpine slopes that may allow for fracture propagations and/or remote triggering. Travel early 
when the crust is hard, but watch out for slick conditions. Stay away from cornices if the sun is 
strong and surface snow becomes moist.

Prepared by Tom Riley