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Avalanche Weather
Fri Jan 09, 2004
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook. Today, commentator David Laskin talks about
avalanches.
A snowstorm blew into the mountains last night, dumping at the rate of two to three inches an
hour. The forecast calls for lingering morning flurries followed by clearing, with brisk
northwest winds. If you're a back-country skier, this probably sounds like your idea of
heaven. This is a classic set-up for avalanches.
Avalanches occur most commonly after rapid and extreme changes in the weather. Heavy snow,
rain falling on snow, a quick rise in temperature -- any of these conditions hitting terrain
with a 30 to 45 degree slope will raise the risk of avalanches. But you don't need a storm to
trigger a slide. Winds just 15 miles an hour can quickly sweep up loose snow, pulverize the
crystals into tiny fragments, and pack them into dense avalanche-prone layers known as wind
slabs. Forget the cartoon image of powder cascading down like a giant pillow fight: the
serious avalanches release brittle cohesive plates of snow that shatter like glass and set up
again like cement. One expert compares these slab avalanches to a magazine sliding off a
table -- with you standing on the cover as it goes over.
So if you want to explore the backcountry in winter, it's essential to check weather and
avalanche conditions before you set out. Wait for the snow to stabilize before embarking on
your excellent adventures. Conditions may not be quite as heavenly as in those first moments
of pristine powder, but they're also far less likely to be hellish.
David Laskin comes to us from Seattle. Our show is funded by Subaru and the National Science
Foundation.
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