Extended Abstract (864K)9.3
High-resolution modeling of the 25 December 2002 Northeast U.S. banded snowstorm
David R. Novak, NOAA/NWS, Bohemia, NY; and B. A. Colle and D. Keyser
The 25 December 2002 (Christmas Day) snowstorm was a historic snowfall event for central and eastern New York State, with storm total snowfall accumulations exceeding 75 cm (29.5 in.) in many locations. These extreme snowfall accumulations were due largely to the formation of an intense mesoscale snowband, found in the comma-head region of a rapidly deepening cyclone along the northeast U.S. coast. This study will explore the capabilities of high-resolution models to simulate the development of banded precipitation in the 25 December 2002 snowstorm. Comparisons between the then-operational NCEP Eta model and versions of the fifth-generation Penn State/NCAR Mesoscale Model (MM5) and the Weather Research and Forecasting (WRF) model will be presented.
Model simulations were run at 12 km horizontal resolution and initialized at 0000 UTC 25 December 2002—approximately 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 2–3 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 20–40 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.
Session 9, Terrain Forcing and Mesoscale Aspects of Winter Storms
Tuesday, 2 August 2005, 3:30 PM-5:15 PM, Empire Ballroom
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