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Analysis of Winter Storm Intensity in the Western US

PI: John Horel
Institution: University of Utah
Abstract:
Deficiencies in the ability of GCM’s to simulate surface temperature and precipitation in regions of complex terrain, such as the western United States, are well established. Since most of the winter snow pack tends to fall during a small number of storms, monthly and seasonally averaged climate statistics are not relevant. The goal of this study is to examine whether proxy synoptic indicators for the intensity of winter storms can be defined that will be less sensitive to the models’ physical parameterizations of boundary layer processes in mountainous regions.

The first proxy to be tested will be daily 700 hPa temperature. 700 hPa temperature in numerical weather prediction models is used extensively by operational weather forecasters to assess whether precipitation in the valleys of the Intermountain West will fall as snow or rain. For mountain ranges such as the Utah Wasatch with peaks near 700 hPa, relatively warm 700 hPa temperature (near 0oC) during a storm cycle tends to be associated with higher water content. Obviously, using only mid-tropospheric temperature will not indicate whether precipitation is actually falling in the actual or simulated atmosphere.

The degree to which present climate simulations reproduce the probability density distribution of 700 mb temperature during the winter season in the western United States as deduced from radiosonde observations will be examined. Then, similar probability density distributions will be developed from GCM simulations using future climate scenarios (carbon dioxide doubling, etc.). After corrections for model biases, the utility of this and other synoptic proxies for inferring sensitivity of winter storm intensity to climate change scenarios will be addressed.
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