There were dramatic differences between operational forecasts of two winter events, with the “Storm of the Century (SOC)” of March 1993 being one of the most successful heavy snow and blizzard forecasts ever for a major winter storm while the “surprise” snowstorm of January 2000 having very limited predictability at all scales. Preliminary experiments suggested that the error growth rate in the “SOC” is smaller than that in the “surprise” snowstorm of 2000. Ongoing research is to determine key dynamical differences in the flows that lead to different mesoscale error growth dynamics between two major extratropical cyclogenesis events and to generalize results of flow-dependent mesoscale predictability concluded from real case studies through explicit simulations of idealized moist baroclinic waves. The study of mesoscale predictability is further extended to an extreme warm-season flooding event in south-central Texas of July 2002. This warm-season event is subtropical in nature with strong conditional instability but weak baroclinicity in strong contrast to mid-latitude extratropical cyclones. It is found that the initial error growth is rapid and occurs at the convective scales but the subsequent upscale growth is relatively weak, perhaps because of the weak subsynoptic features. Through these case studies and idealized simulations, a multistage conceptual model, in which moist processes impose fundamental limits on mesoscale predictability but the error-growth dynamics is strongly dependent on the larger-scale background flow and its attendant dynamics, is being tested.
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