Why do we follow the season history?

Why do we care about the early season snowpack?

Pit Digging

Avalanche forecasters follow the formation of the early season snowpack, as it will be the foundation of the snowpack for the season.

The goal of tracking the snowpack is to have a handle on what kinds of avalanche problems we will see.  Not all avalanches are created equally, and we break these avalanches down into 7 common avalanche problems.  Each problem has unique characteristics.  We think about these problems in regards to where this problem will be found (is it widespread or isolated? On ridgetops or below ridgetops?); the  likelihood of triggering, the size of avalanche & the predictability of the avalanche problem.

In other words we want to “Know Snow”…

By “Know Snow” we mean have a good handle on the current avalanche problems in the mountains.  We can use this knowledge to help choose terrain and make good decisions.  But, snow and avalanches are a natural phenomenon.  No matter how much we know, we’ll never understand it all.  Be a student of the snow and of the mountains, but recognize avalanches can and will surprise the best of us.

If I pay attention to current conditions – to current avalanche problems, to snowfall & wind, I may simply rule out certain terrain based on the avalanche haard.  The same can go for choosing to travel in large, complex terrain with high consequences.

This terrain will only be a go when I have a high confidence the current conditions make it a good choice.

Avalanche Problems

Some Generalizations about snowpack formation:

Shallow snow is weak snow. Deep snow is strong(er) snow.

PWL

We tend to see a weaker snowpack when early season snow falls and then sits for a long, cold, dry spell.

Some weak layers form and stick around for weeks or months.  These persistent weak layers (depth hoar, facets, and surface hoar) form during periods of clear (or cloudy), cold weather, when it is not snowing.

When persistent weak layers are buried in the snowpack, we will likely find persistent or deep slab avalanches as some of the current avalanche problems.

Persistent avalanche problems are tricky.  Obvious signs that the snowpack is unstable may be gone, but the avalanche problem lingers. It can be very hard to tell when the snowpack has become stronger and more stable.  Persistent and deep slab problems cause forecasters to lose sleep.

Storm SnowConsistent early season snowfall is the best way to build a strong snowpack.  With a strong snowpack we are, most likely, only dealing with surface instabilities each time it snows – loose snow avalanches, storm slabs and possibly wind slabs.

When it snows a lot, we see avalanches, but these “storm snow” avalanches are relatively easy to predict – easier to predict than persistent slab avalanche problems.  It storms, there are obvious signs of instability, and avalanches.  Typically, a few days after the storm, the problem is gone.

So What?

Tracking the weather history gives us an idea about what is at the bottom of the snowpack.  Do we have a solid foundation or a snowpack built on a house of cards?  This helps us understand and identify the avalanche problems we can expect to see in the mountains.  This knowledge can be a starting point to choosing terrain.

Here is where the rubber meets the road.  You can see how some of this information comes into play with the planning section of our “Skiers Checklist.”

 checklist

Firewood and Berries:

The only downside to formulating an opinion about what’s out there is the human nature to “see what we are looking for.”

This summer as I was carrying firewood back to my car, a family drove up and asked if I had seen any berries in the area.  I said, “no, just lots of good dry firewood.”

After all, that was what I was looking for.  On my next trip up the hill I noticed that the bushes all around me were bursting with serviceberries.  I was looking for firewood, and didn’t clue into the berries until someone else mentioned them.

Berries

photo: Bruce Smithhammer

The same is possible with avalanche problems.  The trick is to have an opinion on current conditions, but also be open to discovering new information.

by Don Carpenter

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