Model Performance during Explosive Cyclogenesis for Two Cold Seasons
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Analyses and forecasts from the National Meteorological Center NMC were examined over two cold seasons to find forecast errors during explosive and moderate cyclogenesis over the region bounded by 25 cnd 60 degrees north and by 90 degrees west and the eastern edge of the nested grid model NGM display. An explosive cyclone was defined as any cyclone which deepened at least one bergeron during any 24 hr period, while any cyclone which deepened between .5 and 1 bergeron was defined a moderate cyclone. There were 53 explosive and 43 moderate cyclones found during the study. The mean central pressure errors for the NGM 24 and 48 hr forecasts following the maximum 24 hr deepening were 6.2 and 12.5 mb respectively, while the corresponding errors for the moderate cyclones were 2.5 and 6.0 mb. The correlations between the predicted and analyzed deepening rates were higher for the explosive cyclones. The NGM forecasts of both the explosive and moderate cyclones showed a significant southwest bias which grew with time. The bias was due to the NGM forecasting the cyclones to move too slowly. The performance of the NGM to forecast explosive cyclogenesis events in terms of the critical success index CSI has not changed much over the last three years. The CSI scores for the 24, 36, and 48 hr forecasts were .62, .53, and .43 respectively. The correlation between the predicted and analyzed 12 hr deepening rates during explosive cyclogenesis improved slightly over those reported in previous studies.