The Influence of Orography on an East Coast Storm,

A high resolution, limited area version of the NCAR GCM is used to simulate the March 14, 1975 east coast storm. Based on climatological data, synoptic experience, and an examination of numerous cases, this cyclone was chosen because it seemed to have been strongly influenced by the Appalachian Mountains. The storm was investigated in detail and is briefly described. The NCAR GCM is also described briefly. Two simulations are made with the 1.25* resolution, 24 layer version, the first simulation including orography and the second incorporating a uniform land elevation of 10 meters above sea level. Neither of the 36 hour forecasts exhibited exceptional skill in this situation. It is doubtful that the simulations could be of much use in analyzing the more impoytant aspects of the observed storm. However, the model did appear to be sensitive to the inclusion of orography, producing a ridge-trough couplet east and west of the mountains, respectively, when orography was included. Although this perturbation "improved" the forecast, the observed couplet is due more to the passage of the primary center west of theimountains, whereas the model perturbation is believed due to an upslope/downslope divergence/ convergence effect. A cold perturbation in the temperature field also resulted from the incorporation of orography. Lying east of the mountains at low levels, this perturbation is believed due to cooling accompanying orographically forced upward motion. Precipitation differences between the two cases were, in general fairly small. Direct orographic forcing, while perceptible, was judged to be of significantly lesser importance than the indirect effect of the mountains in altering the storm track and larger scale circulations.