[MCR] Avalanche Ratings in Spring Conditions

[Public Mountain Conditions Report]

Every year it seems that there is a debate of what to call the avalanche
danger in the public bulletin when true spring conditions have arrived. IE:
frozen solid and LOW danger in the mornings rising to wet and unstable HIGH
or EXTREME conditions by late in the day, but there is only one  forecast
rating for the 24 hr period. Should the rating default to the highest
possible danger to warn people that avalanches are almost certain at some
time in the day,  or default to the lower end because travel while frozen
has almost no avalanche danger, or pick somewhere in between?

At various times the terms "Variable", "Not Rated*(*see text, )", and
"Spring" have been used to overcome this dilemma rather than pick a single
rating, but this approach is not standardised to the North American Danger
Scale

It is important to remember that avalanche danger varies both spatially
(over terrain) and temporally (over time). We have no problem understanding
that the danger may be different in different places in the terrain and can
certainly think about danger improving or decreasing over time periods of
several days. The issue with spring conditions is that the temporal swing
in danger happens rapidly within the period of 24 hrs normally covered by a
public bulletin, (or  a commercial  operational forecast), so it really is
a question of timing and aspect to determine the specific danger.

When I am asked how the danger can be rated as "LOW" when there have been a
number of large avalanches observed on a given day, I think about it this
way.  "Where in the terrain would it be possible to go and not be subjected
to avalanche danger on that day, and how long during the day would it be
possible?" (space and time). If there have been clear cold nights with a
good solid freeze and the answer is that you could go almost anywhere and
have solid snow conditions and have them for a reasonable amount of time,
then obviously the danger must be LOW. The bulletin user has to understand
that timing is part of the equation. Conversely, if there was cloud cover,
very little freeze and there would likely be stability problems during the
majority of the day, the danger would have to be higher.

"LOW" does not mean "NO AVALANCHES" It takes into account the fact that
there is a swing in danger during the day, but that for the average
bulletin user who can understand that ice melts when heated above zero, the
conditions are excellent and it is the time to take advantage of the
conditions.

This last week has been one of the best weeks of ski touring in the Rockies
for some time. Excellent freezes with very little in the way of avalanche
concerns and good travel. We use the headline to highlight the importance
of good timing, and give the users the "Green Brick". Go have some fun. It
is the right time to do the big trips. Use your head , start early, keep an
eye on the temperatures and the faces that are exposed to the sun and
enjoy!  Come home before the avalanches start....and the danger to you will
be LOW.

Brad White
Visitor Safety Programs Specialist
Mountain Guide