OR-AMS Meeting Summary

“Mountain Weather and Recreation” by Matt Zaffino, KGW-8

Given the high profile mountain climbing accidents and rescues this last winter in the Cascades, we wanted a talk about mountain climbing weather. So, 29 guests gathered at the Old Wives Tales restaurant in east Portland to listen to a local expert: Matt Zaffino.

Matt reviewed the basics of mountain weather and asked the audience: Why do climbers get into trouble? These factors are crucial (and sometimes combine): (1) “Weather window” is critical (i.e., timing), (2) Any accident can slow you down, (3) Speed (being too rushed). Any factor, or in combination, can lead to a compounding of errors, which can be fatal. For example, snow caves are hard to dig out, so bringing a tent is a big time saver, and time saved is more time given for your “weather window.” Good preparation and protection is a must, as winds often exceed 100 mph at high elevations. The Cooper Mountain route on Mt. Hood is the most dangerous.

Winter weather is often good for mountain climbing. Specific weather events can turn benign conditions into a life-threatening drama. On February 24, 2007, Crystal Mountain Ski Area (6700 feet) on Mt. Rainier saw 49 inches of snow in four days (with 13 inches in one day). One skier died as he was caught in an avalanche in an “out of bounds” area. On February 25, 2007, at Mt. Hood Meadows, the Heather Woods Ski Area saw 7 inches of snow in one day. Two skiers on a steep slope (45 degree) were caught in an avalanche when a two-foot slab of snow broke off and slid down. They survived.

An avalanche forms when a slab of snow develops over a frozen layer (snow previously melted then refrozen) due to wind loading, then a trigger (e.g., sound or vibration) serves as a the catalyst for the snow slab to break off, slide down, and pick up more loose snow. An avalanche slab can be as hard as rock, as the avalanche picks up and mixes ice crystals within the snow layers.

Backcountry skiers and snow-mobilers account for 50% of avalanche fatalities. In general, January is the peak for avalanche incidents. December is the peak month for the Pacific Northwest, and, surprisingly, June (due to more folks out in the backcountry and sometimes cold spring conditions where melt and refreeze is more common), based on 1975-2005 data. Good climbing weather indicators – lenticular clouds over mountaintops (suggests impending change), cloud level, low relative humidity, and vertical wind profile data. For real-time data from the NW Avalanche Center: www.nwac.noaa.gov.

After the talk concluded, Matt answered several questions. We appreciated Matt sharing his expertise and cool powerpoint slide show with us over a good dinner.

Note-taker: Kyle Dittmer, OR-AMS President