Spring Touring

Terry O’Connor, MD

SOME KEY SPRING TIME CONSIDERATIONS:

Spring is a wonderful time for ski touring. Warm weather and sunny skies after fast moving storms can be a recipe for a great time. The challenge is to not forget about avalanches as you’re out skiing in the sunshine.

On a recent bluebird day touring in Norway we observed numerous examples of the types of hazards that can be seen or develop on a single day tour. Here’s a little picture review  . . .

#1 DON’T FORGET ABOUT EXISTING PROBLEMS

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When the sun first comes out, the explorers in us often want to tap high into the alpine when the weather is good. In their thirst for a fair weather line in the alpine, this group forgot about a persistent weakness in the snowpack and the previously observed avalanche activity at similar aspects and elevations seen in the days before.

#2 EVEN THOUGH IT IS SUNNY DON’T FORGET ABOUT THE NEW SNOW

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Dry loose sluffs of new snow seen in the steep terrain. Undoubtedly more remains to be triggered if you ski similar pitch and aspect. What’s up with the ski tracks on the right? Did Odin himself descend from the heavens for a pow lap? Well perhaps something else happened overnight to fill in the tracks which brings us to the next . . .

#3 RECENT WINDLOADING

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Even if there has been no recent precipitation remember a wind storm can still move a significant amount of snow around in the alpine zones you wander into on those good weather days. Enough new snow loaded cross slope in this zone to trigger a release.

#4 SOLAR ACTIVITY

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Once the sun hits solar aspects small ‘pinwheel’ or larger loose wet avalanches can start to occur. How big are they going to be? Hard to say, but read on for a few considerations.

Springtime often brings melt-freeze cycles. During the day, the air temperatures rise to above freezing and the snowpack melts. At night, the temperatures drop below freezing and the snowpack freezes. This cycle of daytime melting and night time freezing can go on for days or even weeks.

Things to think about during a melt-freeze cycle:

Did it freeze last night? If yes, how long did the temperature stay below freezing?

This can offer a sense of how thick the freeze is. Knowing how thick the freeze might be is important, as conditions can change rapidly in the springtime. If it froze for only an hour, the window for safe travel is going to be shorter than if temperatures were below freezing for 10 hours. In other words a good thick freeze buys you more time for that snow to be in the sun before it can weaken.

If there was no freeze overnight, be careful. The snowpack did not regain strength, but continued to lose strength overnight. Often, significant avalanche activity occurs after the 2nd or 3rd consecutive non-freezing night.

#5 CORNICES

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This cornice fractured with the warming temps, triggering a slab avalanche below. Give these features extra distance and respect as the sun hits and the air temp increases.

In the spring, strong solar radiation and/or warm temperatures can weaken the snow in a matter of minutes. Avalanche danger can change from LOW to HIGH very quickly. Be alert to changing conditions and be prepared to adjust your travel plans accordingly.

By the time we finished our day we saw at least 10-20 new avalanches triggered by the new strong spring sun.