Cold Fronts Aloft and the Forecasting of Precipitation and Severe Weather East of the Rocky Mountains

Abstract

Brief descriptions are given of four cases that illustrate the important role that cold fronts aloft (CFA) can play in producing significant weather cast of the Rocky Mountains. In all four cases, the CFA, and its associated short wave, were located ?200?300 km ahead of a surface trough. Precipitation (and in some cases severe weather) developed along the leading edge of the CFA. The nested grid model generally did a good job of locating the CFA. Analysis of absolute momentum confirms that these features were fronts, in a dynamic, as well as a thermodynamic sense. A conceptual model for CFA is presented. In the cases examined, this model provides not only a useful picture of the distribution of clouds and precipitation associated with CFA, but also means for locating them. It also helps to define a major class of systems that do not fit the Norwegian cyclone model. Therefore, it should help in the identification of CFA and in improving the forecasting of precipitation and severe weather associated with them.