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Paul H. Ruscher and Thomas P. Condo

Abstract

The unusual case of a rapidly developing land cyclone that occurred on 15–17 November 1989 over the United States and Canada is investigated to determine the physical mechanisms responsible for its development. Hourly surface and 12-h upper-air data are analyzed for this storm for the 36-h period beginning on 0000 UTC 15 November.

Findings reveal that surface-based frontogenetic forcing and the diabatic effects of latent heating were primarily responsible for the initial development of the system. Proper positioning of the surface low with respect to a 500-mb short-wave trough and 250-mb jet streak yields the greatest deepening of 13 mb in 12 h at a later time. It is suggested that frontogenetic mechanisms contribute to development of this system prior to any favorable organization of the large-scale upper-tropospheric dynamic forcing.

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Paul H. Ruscher and Thomas P. Condo

Abstract

The relatively rare case of an explosive land cyclone that occurred on I5–17 November 1989 over the United States and Canada is investigated to determine the physical mechanisms responsible for its development. Hourly surface and 12-h upper-air data are analyzed for this storm for the 36-h period beginning on 0000 UTC 15 November. The system appears to develop through favorable positioning of the surface low with respect to a 5OO-hPa short-wave trough and 250-hPa jet streak and yields the greatest deepening of 13 hPa in 12 h.

Through an analysis of the terms in the quasigeostrophic height tendency equation, quasigeostrophic theory is deemed to be qualitatively inaccurate in diagnosing the development of this system. The performance of the National Meteorological Center's (currently known as the National Centers for Environmental Prediction) operational models is viewed, and errors in model forecasts of surface low position and intensity are attributed in large part to faulty initialization. A companion study examines the thermodynamic and frontogenetical aspects of this case.

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