Several people have emailed me questions about La Nina in the last couple weeks. The general vibe: people want to know what a La Nina winter will mean for avalanche safety in Washington State.
From a meteorological perspective, a La Nina winter is colder and wetter, which means larger, more frequent storms, and lots of snow in the mountains. However, La Nina has no mysterious influence on the snowpack itself. Prolonged cold temperatures, which can occur during any winter, will either produce new snowpack instability or allow existing snowpack instability to linger for longer periods of time. Large storms, which can occur during any winter, always produce instability. Rising temperatures during storms always produces instability. Some or all of these events may happen more often in a La Nina winter, but the snow safety rulebook won't change. You can learn more details about La Nina years on Amar Andalkar's excellent web site.
What about avalanches during La Nina winters? The last La Nina winter was 2007-2008, and there were a record number of fatalities in Washington State. For example: there were 5 fatalities in Washington State during a single weekend in early December 2007. In North America, there were 14 fatalities during the month December. That's basically one fatality every other day.
So, where were we? ...Frequent storms and lots of snow in the mountains... Sounds perfect, right?
Yeah, it's perfect ... but like everything wonderful, there's a catch. According to The Avalanche Handbook, "direct loading by synoptic scale weather events causes most avalanches". In other words, lots of storms means lots of potential for skier-triggered avalanches. Avalanches that occur during storms are referred to as direct-action avalanches, and these avalanches occur during a storm or within 24-72 hours after the storm ends. It's a good bet that public avalanche bulletins in North America will often forecast High avalanche danger during the upcoming winter.
What's your strategy for touring on days when avalanche danger is High? Do you have a list of trips for different levels of avalanche danger? ( Feel free to post tips in the comment box. )
The Take-Away
- There will be frequent storms.
- Avalanche danger will be High during and after these storms.
- Start thinking about terrain choices for the winter.
- Always choose terrain appropriate for current conditions.
- Develop a list of "go to" terrain that is appropriate for high avalanche danger.
- Plan like your life depends on it. ( Because it might. )
- Take an avalanche safety course if you haven't already done so. United States / Canada
- Hire a guide for big trips.
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