I made a cut and paste error and missed the last part of what I wanted to
say in my previous mid-season review. Here it is:
THE FEBRUARY 20 LAYER
The cold snap in early- to mid-February created a variety of surfaces
which will be problematic in the coming storm cycle. This layer consists
of:
? Suncrusts on sunny aspects (more so on steeper slopes) of all
elevations except perhaps the highest alpine regions. In many areas,
these suncrusts have a thin layer of weak, sugary facets lying on them.
There?s also patches of surface hoar on the suncrusts, especially at
lower elevations and areas sheltered from wind.
? Wind crusts and slabs in exposed treeline regions and alpine regions
where the sun didn?t create crusts. In most places these crusts have the
facets mentioned above on top with some areas of surface hoar also.
? A thicker layer of weak, sugary facetted snow below treeline with
surface hoar mixed in, especially lower elevation sheltered areas.
On or about Feb 20, this layer was buried and it is now anywhere from 30
to nearly 100cm deep below relatively low density snow that has not yet
settled very much. The first round of avalanches on this layer started
Thursday, February 23 in the southern Selkirks, where the new snow is
deeper and where the wind had created soft slabs.
With ongoing new snow over the next couple of days and forecast high
winds, this layer is almost certain to be a good avalanche producing
machine; certainly in the short term?and it has the potential to be
another layer that persists for a long while. Only time will tell if
this layer become persistent, but in the interim, it?s not something to
take lightly: it will produce avalanches big enough to be a problem in
and of themselves and could provide large triggers which might activate
the deeper layers mentioned earlier.
RISK MANAGEMENT FOR THE FEB 20TH LAYER
Managing risk associated with the Feb 20th layer will be very much like
what I discussed in the Below Treeline, Treeline, and Alpine discussion
earlier. The thing that?s going to be tricky with this layer, and the
reason I discuss it separately from the rest of the issues, is that it
may catch people by surprise because it?s been buried for a few days now
but has been largely dormant.
I think it has not become active because there?s not yet (or we?re just
approaching) critical loads. Even though there?s been quite a bit of
snow, it?s been cold, light stuff so far so it hasn?t the weight that
warmer denser snow contains. In addition, the snow so far hasn?t yet
become very cohesive and will not carry propagation very far. That is,
it?s not yet a real slab in many areas.
This is all going to change; in fact, the change has probably already
started. With the new load, increasing winds, and a rapid warming trend
just around the corner, the new snow on top of the Feb 20th layer will
quickly become a cohesive slab through a variety of influences:
? New snow adds weight and promotes settlement which may produce
slab-like properties.
? Wind will create slabs as it moves snow from windward locations to lees.
? Warming temperatures will promote settling and will increase cohesion
(and slabbing) in the upper part of the snowpack.
? It?s getting to the time of year where solar radiation can add a lot of
heat to the snow very quickly and that weakens any bonds that might be
holding things together.
Starting Tuesday, the weather will break, perhaps for a couple of days
and it will be tempting to head into the mountains. I think regardless
of where you are or what the local weather condition, it will be prudent
to be very careful when you go back out there over the next few days and
perhaps even into next weekend or longer.
Karl Klassen
Mountain Guide
1735 Westerburg Road
Revelstoke, BC V0E 2S1
Canada
kklassen@xxxxxxxxxxxxxx
250-837-3733
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