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Cliff Mass - Weather of the Pacific Northwest

Chapter 8 - Mountain-Related Weather Phenomena

p. 173-4: This chapter has a short section on avalanche weather, including a description of the 1910 Wellington train disaster and a photograph of two locomotives toppled by the avalanche.

Chapter 12 - The Evolving Weather of the Pacific Northwest

p. 239: Climate records indicate that the Northwest became somewhat warmer and wetter during the years from 1920 to 2000, but year-to-year variability dwarfs the small increasing trend during the period. The trend in mountain snowpack depends on the period over which it is taken, with recent short spans showing little trend, while 40- to 60-year trends suggest significant declines. After examining the possible effect of the Pacific Decadal Oscillation (PDO), the author concludes that there is no clear indication that global warming induced by mankind has caused a reduction in Northwest snowpack. Yet, he writes, "scientists have great confidence that global warming forced by human impacts will have a major influence on Northwest weather and climate, including snowpack, during the twenty-first century."

p. 242: Photos on this page illustrate the dramatic reduction in size of the South Cascade Glacier in the Cascade Mountains between 1928 and 2000.

p. 247: Based on analysis of global circulation models (GCMs), the Intergovernmental Panel on Climate Change (IPCC) estimated in 2007 that the planet will warm roughly 2.5-10.5 degrees F (1.4-5.8 degrees C) between 2000 and 2100. The warming is expected to be non-uniform, with the Arctic heating up the most and land areas warming more than the oceans. A major project of the University of Washington has been to run high-resolution regional prediction models over nearly a century into the future, making use of information from the GCMs. These regional models can take into account local geographic effects to predict the implications of global warming for the region.

A simulation using the MM5 regional model shows 1-2 degrees F more warming over the Olympics, Cascades, and eastern Washington than the 1-3 degrees F of warming predicted by the ECHAM GCM. "An interesting detail," notes the author, "is that the largest warming is on the lower and middle mountain slopes." The enhanced slope warming is probably due to melting of the snow and ice by generally warmer temperatures. The amount of water in the snowpack during the winter months is expected to decline by 10-25 percent by 2050 on the lower slopes of the Cascades and B.C. Coast Mountains, when compared to the 1990s.

The MM5 model predicts a 30 percent reduction in snowpack during the late winter and early spring between the 1990s and 2050s. By the 2090s, the loss of snowpack is predicted to decline 75 percent or more during the late winter and early spring. "The implications of these snowpack reductions are profound," writes the author, including "the probable ending of skiing on the lower-elevation slopes such as Snoqualmie Pass and greatly reduced water availability during midsummer and early fall."

By contrast, the high-resolution simulations predict that springtime (March-May) low clouds may actually increase west of the Cascades under global warming. Since clouds reflect the sun's radiation back to space, this will result in cooler spring weather over the western lowlands, similar to weather currently found in northern California in late spring and summer.

Regional climate simulations suggest that local changes in precipitation will be small under global warming, with slight increases in annual precipitation and the greatest enhancements during the late fall. "Although annual precipitation totals do not appear to change greatly under global warming, the type of precipitation evolves substantially during the winter, with snow replaced by rain at lower and intermediate elevations."

Appendix - Pacific Northwest Weather Resources

p. 265: The appendix lists resources (on the web and published on paper) for current weather conditions, the latest forecast, climatological conditions, and the long range weather outlook. The author also lists research literature on Northwest weather.

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Last Updated: Thu, Sep 13, 2012 8:28:46 PM