Development of a Rapidly Deepening Extratropical Cyclone over Land. Part II: Thermodynamic Aspects and the Role of Frontogenesis

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.