20th Conference on Weather Analysis and Forecasting/16th Conference on Numerical Weather Prediction


A different beast: An example of a major midlatitude cyclogenesis event over the Intermountain region of the Western United States

Jason C. Shafer, University of Utah, Salt Lake City, UT; and W. J. Steenburgh and G. L. West

An observational analysis of a major Intermountain cyclogenesis event dubbed the "Tax-Day Storm", which occurred 15 April 2002, is presented. The analysis is based on surface observations from MesoWest networks, and traditional upper-level data upon which quasi-geostrophic and potential vorticity diagnostics were computed. This event caused over 3 million dollars of damage, brought heavy rain and snow, prefrontal winds of 30-35 m/s, and blowing dust that forced the closure of state highways and interstates. The cyclone deepened 14 hPa over 18 h as the surface cold front underwent intense frontogenesis over northern Utah and Nevada. Although cyclogenesis ensued from a classical perspective as a strong upper-level system moved overhead of a baroclinic zone, this event departed significantly from the traditional midlatitude cyclone structure. For example, the space (500-700km) and time (12-18h) dimensions of this event were mesoscale, and the distribution of clouds and precipitation was mostly postfrontal. This poster will examine the factors which may have contributed to the cyclogenesis, strong frontogenesis, and unique structure, including an extremely dry prefrontal airmass, and distortions of kinematic and thermodynamic fields by complex terrain. The Tax-Day Storm had similar characteristics of other major Intermountain cyclones; thus, this analysis may be used to improve analysis and prediction of such events.

Poster Session 1, Monday Posters
Monday, 12 January 2004, 2:30 PM-4:00 PM, Room 4AB

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