An Analysis of NMC's Nested Grid Model Forecasts of Alberta Clippers

Abstract

Abstract Forecasts of Alberta Clipper–type cyclones defined as cyclones that move southeastward from regions of western Canada into south-central Canada or the north-central United States before moving eastward to the coast of North America, were studied using the National Meteorological Center's Nested Grid Model (NGM). All available NGM forecasts between 1 January 1988 and 31 December 1992, excluding the months of June, July, and August, were analyzed. The 5-yr sample included 59 Alberta Clippers. For each cast, the cyclone center position and central pressure were recorded for the NGM's initialization (0 h) and for 12-, 24-, 36-, and 48-h forecasts for each available run. Average cyclone position errors ranged from 140 km, with a standard deviation of 183 km at 12 h, to 339 km, with a standard deviation of 407 km at 48 h. Average central pressure errors ranged from 0.0 hPa, with a standard deviation of 2.5 hPa at 12 h, to 1.0 hPa, with a standard deviation of 5.7 hPa at 48 h. East of 84.0°W, cyclones v...