HR: 1340h
AN: GC33A-1247    [Abstracts]
TI: Snow Avalanche Climate and Extremes of the Western United States Mountain Ranges
AU: * Mock, C J
EM: mockcj@sc.edu
AF: Department of Geography, Department of Geography University of South Carolina, Columbia, SC 29208 United States
AU: Birkeland, K W
EM: kbirkeland@fs.fed.us
AF: U.S. Forest Service National Avalanche Center, P.O. Box 130, Bozeman, MT 59771 United States
AU: Shinker, J J
EM: jshinker@uwyo.edu
AF: University of Wyoming, Department of Geography University of Wyoming A&S 206, Laramie, WY 82071 United States
AU: Bergen, M
EM: Michelle.Bergen@trimble.co.nz
AF: Trimble Navigation Ltd, New Zealand, Christchurch, PO 8729 New Zealand
AB: Previous snow avalanche climatic research on the mountains of western North America, based primarily on field data, have traditionally classified three main avalanche climate zones: coastal, intermountain, and continental. The coastal zone of the Pacific mountain ranges is characterized by abundant snowfall, higher snow densities, and higher temperatures. The continental zone of most of the Rocky Mountains is characterized by opposite conditions and extensive faceted crystal growth. The intermountain zone of Utah, Montana, and Idaho is intermediate between the other two zones. We revisit a quantitative assessment snow avalanche climate of the western mountains based on Westwide Avalanche Network data, encompassing mostly the period 1969-1998, and assessed the synoptic climatic conditions and snowpack processes responsible for continental and coastal extremes. A binary seasonal classification, based on avalanche thresholds of snowpack and climatic variables, quantitatively confirm the existence of the three major climate zones. The winter of 1985-86 exhibited the most widespread spatial shift towards more coastal conditions, and the winter of 1976-77 exhibited the most widespread continental shift. Height anomalies at 500 mb explain many of these spatial changes at monthly to seasonal timeframes, but examination of daily plots of weather and avalanche variables during seasonal extremes also illustrate the importance of understanding snowpack and climatic variations that occur at daily to weekly timescales, which also generally correspond to avalanche hazard and accident extremes. A principal components analysis on daily data for selected Westwide sites indicate different combinations of climatic and snowpack variables that are conducive for big avalanche events. Composite anomaly maps of 500 mb heights reveal that strong southwesterly flow is responsible for many avalanche extremes, but some sites are exceptions due to the influence of topographic features on large-scale atmospheric circulation.
DE: 0468 Natural hazards
DE: 0742 Avalanches
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 3364 Synoptic-scale meteorology
SC: Global Climate Change [GC]
MN: Fall Meeting 2005