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Model simulations were run at 12 km horizontal resolution and initialized at 0000 UTC 25 December 2002approximately 19 h before band development. All three models (Eta, MM5, and WRF) accurately predicted rapid cyclogenesis with forecast surface cyclone tracks within 50 km of the observed track; however, the models underpredicted the cyclone intensification, especially the Eta and MM5. Despite various strengths of the surface cyclone, all three models exhibited band development in central New York within 2 h of the observed time, suggesting some degree of predictability in this case. However, the initial band position in all three models was as much as 100 km too far southeast, and band dissipation occurred 23 h prematurely in all three model simulations. Furthermore, all models underpredicted precipitation within the banded region (as much as 50% in the Eta model forecast).
Investigation of the physical processes responsible for the simulated precipitation bands revealed that all three model runs exhibited a 700-hPa frontogenesis maximum oriented parallel to the simulated band, with saturation equivalent potential vorticity values less than 0.25 Potential Vorticity Units located above the frontogenesis maximum. The combination of frontogenetical forcing and weak moist symmetric stability supported a narrow, sloping ascent maximum (exceeding 0.5 m s-1), which is consistent with theory and observations. Although one might expect the forecast precipitation band to be directly beneath the maximum ascent, all three simulations forecast the band 2040 km farther northwest. It is hypothesized that precipitation lofting and drift may account for at least part of this displacement in the model simulations and presumably in the real atmosphere.
This case shows that high-resolution models are capable of simulating the physical processes responsible for mesoscale bands. Future research will draw on higher-resolution simulations to explore the impact of model resolution on the prediction of mesoscale bands. Hydrometeor trajectories also will be used to diagnose precipitation lofting and drift in the model simulations.
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