February 26, 2006
Seeing as its about half way through the season, I thought I might
provide my take on how things look at the moment and some ideas for
where we might go from here. The following is based on spending two
weeks a month guiding clients on the west slope of the central Monashees
(just south of Three Valley Gap) during which time I look at and distil
daily data from all over BC and Alberta to help me decide where and how
to ski with my guests. In my two weeks off I change gears completely and
spend 8-10 days in an office with a crew of other professional avalanche
forecasters producing public forecasts for vast regions of BC.
The following is largely representative (in my opinion) of the Columbia
Mountains from the Cariboos in the north, through the Selkirks and
Monashees to the US border. The heavy snow areas on the west slope of
the Rockies are probably somewhat similar to the Selkirks, while the
dryer areas on the divide and east have a shallower snowpack to which
the following probably does not apply. Perhaps someone who has been
working in and watching the east side of the Rockies closer than I might
want to put together a bit of a summary for that region. The west side
of the Purcells is probably similar to what I discuss here, while the
east is somewhat shallower and maybe a bit more like the Rockies. Ditto
the Kootenays?
What follows is my personal opinion and is somewhat long and
involvedsorry. Ive been working on it on and off for the last week or
so and dont feel I want to oversimplify, nor do I think I can be more
concise when discussing such big-picture issues over such a large time
frame. This is broad brushstroke stuffnot intended for specific slope
by slope decisions, but something to keep in mind in the general
planning phase of a trip and when watching big-picture trends.
BELOW TREELINE CONDITIONS
In areas sheltered from wind, the danger of avalanches remains relatively
low. Short periods of increased danger will accompany major dumps of new
snow but these will generally settle out relatively quickly and no major
weaknesses exist deeper in the snowpack. Watch for upside down snow,
that is warmer/higher density snow on top of colder, lower density snow.
You can tell when this happens because it becomes difficult to travel as
your skis go deep and get stuck every step or two as they plunge under
the snow. This condition generally settles out quite quickly (24-36
hours) and what was incredibly twitchy today may be just fine by
tomorrow. My biggest concern below treeline in recent weeks has been big
treewells, especially on steeper slopes where skiing produces loose
sluffs.
BELOW TREELINE RISK MANAGEMENT
Ski with a partner at all times, plan your turns ahead (looking at the
openings between the trees!), and never, never make a turn above the
tree: always initiate your turn beside and finish your turn below a tree.
The big thing to be aware of below the treeline is that, due to deeply
buried weak layers on alpine slopes, the runout zones of large avalanche
paths are a place to be very cautious this winter. Read the discussion
below regarding alpine regions. In short, unless you are aware of a
given paths avalanche history for the winter, I advise not hanging out
in avalanche path runout zones with alpine start zones above. Avoid
runout zones as much as possible. If you must cross, do so quickly, go
one at a time, and consider turning back if conditions are favourable
for cornice fall or avalanches in the alpine.
Theres lots of great and safe skiing below treeline with some common
sense and basic precautions.
TREELINE CONDITIONS
Few significant weaknesses deep in the snowpackthe exception being
shallow snowpack areas (less than 1.5 to 2 metres or so on average).
Slabs do exist in areas exposed to wind. Some of these formed prior to
the most recent snowfall and are buried. Others formed during the last
storm and are on the surface. These slabs will likely settle down in a
few days but care will be required over the coming stormy period,
especially when the sun comes out between snowfalls and feels strong and
if air temperatures (which have been mostly cold for a few weeks now)
warm up. Theres been a bunch of new snow (there was 60cms on my
driveway in Revelstoke this morning) and, if the wind has not yet been
moving that snow around, it probably will soon. When winds blow do
arrive at treeline, the slabs there will increase in size and number and
you can expect any problems that do exist or which are created anew,
will last a little longer rather than go away sooner.
BELOW TREELINE RISK MANAGEMENT
Lots of good skiing in sheltered areas and on smaller planar slopes where
steep convex rolls or sharp transition are absent, away from windloaded
(especially crossloaded) areas, and out from under large alpine slopes
or big cornices above. Of note here: one of the biggest cornice failures
I saw in the last round of such events in the Monashees, was a treeline
feature.
ALPINE CONDITIONS
The big slides weve been seeing on and off for much of the winter are
often failing on weak layers from November and December now buried deep
in the snowpack. Its difficult to initiate failure at these layers
because they are so deeply buried, thus the need (generally) for a
fairly major trigger.
During the recent cold snap there have been fewer reports about failures
deep in the snowpack on the December and November weak layers. Those
weak layers may be sleeping now, but they will almost certainly wake up
again before the winter is over, I suspect reactivity will cycle with
the weather.
Cornices, which grew rapidly during Januarys storms, remain a concern.
Cornices have been falling off with regularity when temperatures change
(from cold to warm and warm to cold), during warm spells (late in the
day), after snowfall and wind events, and sometimes just from solar
radiation on a sunny day. Cornice triggered avalanches earlier in the
winter have been two to three and more metres deep, hundreds of metres
wide, and running more than a kilometer downhill. In addition to
cornices, large avalanches on deeply buried weak layers could be set off
by other large triggers like rockfall, icefall, and smaller avalanches
smacking a slope from above.
The exception to the big trigger requirement mentioned above is in
places where the snowpack is shallower or variable in depth. Smaller
triggers like skiers, boarders, and sledders have been able to initiate
significant slides in places where there are alternately scoured and
loaded areas (windward and crosswinded slopes, for example), where there
are major terrain transitions (such as pronounced convexities), where
rocks poke through, or where you see underlying terrain features
reflected by the overlying snowpack (because the snow is not deep enough
to even out the terrain features beneath).
The large natural and human triggered slides I mention above have been
isolated and intermittent, but when they go, theyve been going very
big; in some cases overrunning historical avalanche boundaries (for
example, taking out mature timber at the bottom and sides of runout
zones).
ALPINE RISK MANAGEMENT
No one that I know of or have spoken to recently is digging pits that go
down to the deeply buried alpine weak layers. They are simply too deep
to get to and even if you went there, carrying out meaningful tests
would be difficult or impossible. An experienced colleague recently
commented on this, saying something like (Im paraphrasing here) with
these persistent and deeply buried weak layers, well probably not be
forecasting stability and hazard by making snow observations or
stability tests; rather we will assess them based on avalanche
activity . What he means is professionals will be watching carefully for
signs that large triggers are likely or avalanche activity involving
these deep layers is starting up again and as soon as that happens,
theyll retreat to safer terrain until the potential drops off again.
Big trigger potential and large avalanche events have been cyclical and
largely related to the weather. During the recent cold weather, the
number and size of avalanches reduced. After a few days passed with
little or no activity, I carefully ventured onto larger alpine features,
always mindful of what lay above me and remaining very aware of places
with variable depth snow and terrain traps. For the rest of the winter
Ill be pulling back every time it warms up, whenever significant new
snowfalls occur, if winds load snow onto larger, steeper slopes, and
when solar radiation feels strong. Ill wait to see what happens and if
it appears that no cycle is starting up or if a cycle starts up then
dies off again, Ill once again venture back into the bigger terrain,
after a period of little or no activityslowly and with caution at first.
There have been a series of very close calls (several partial and full
burials) and one fatal avalanche in recent weeks. Many of you will not
have heard about the close calls as they dont make it into the media.
Having looked at photos of the events and reading first person accounts
about some of them, it is clear to me there are some common threads.
Keep the following in mind when you are out in the mountains over the
coming weeks:
" All these incidents have involved relatively large slides, failing
quite deep, triggered by skiers or sledders.
" Almost without exception, recent avalanches involving close calls or
fatalities have occurred in shallow snowpack areas (east slopes of the
Coast Range, Purcells, and Rockies).
" They all involve the kind of snowpack and/or terrain that gives me the
willies: shallow snow with lots of rocks sticking out, big drifts
running up and down the fall line behind terrain features and lines of
trees, and lots of variation from deep to shallow snow on the same slope.
" They all involved recreational parties who probably were not
knowledgeable about the avalanche history of the slope they were on.
" With only one exception (a flat light, overcast day) that I can think
of, these events occurred on fine weather days. Good weather often
encourages a positive attitude and gives people a false sense of
confidence. Stormy weather tends to keep people on the couch or on
mellower terrain in the trees. But this year, the underlying condition
causing these accidents persists, regardless of whether its a bluebird
day or youre in the clag with zero visibility.
While the chances of being involved in one of the large avalanches I
mention above are probably relatively low (especially if you use some
basic precautions), if you get mixed up with one you will not outrun or
escape itit will be a fatal event. We are on the cusp of a period of
stormy weather interspersed with calmer, clearer spells. Skiing will be
great and there will be days when the weather is excellent. But
remember, things are changing and its in times of transition when many
of these bigger events have historically occurred this yeardont get
caught with your guard down.
_______________________________________________
These observations and opinions are those of the person who submitted them. The ACMG and its members take no responsibility for errors, omissions, or lapses in continuity. Conditions differ greatly over time and space due to the variable nature of mountain weather and terrain. Application of this information provides no guarantee of increased safety. Do not use the Mountain Conditions Report as the sole factor in planning trips or making decisions in the field.
Please check out http://acmg.ca/mcr for more information.