Examination of WEF-ARW thunderstorm simulations in northern New England

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Heeps, David R.
Convective initiation and development in New England can become complicated due to the underlying topography of the region. Not only can the genesis location of thunderstorms be difficult to predict, but their evolution can be just as challenging to determine. Previous research of northern New England convection found that there are preferred regions for convective initiation with respect to large-scale flow. Another previous study also gave some explanations as to why thunderstorms favor these initiation regions. This study utilizes the WRF-ARW numerical model to further investigate these preferred convective initiation regions. The model simulations were conducted using two nested grids with 4-kmand 2-km horizontal resolutions. Four case studies, two within southwest(SW) and two within northwest(NW) mean flow, were chosen to compare model simulations of these events to observed analyses. Within the model results for both SW cases, convective initiation occurred within areas of frequent thunderstorm genesis as identified by previous research. Belge (2007) referred to these genesis regions as areas of typical" thunderstorm initiation. The WRF simulation contained similar features to the observations. A lee surface pressure trough was apparent through Oxford and Franklin counties in Maine. This trough led to convergence within the "typical" genesis region creating the lifting mechanism for the convection to initiate and develop. The NW cases contained differing results. One case featured a surface pressure trough similar to the SW cases that led to convergence needed for convective initiation. The other case exhibited a synoptic-scale pressure trough over New England and convergence within this trough appeared to be enhanced where the convection initiated. Other miscellaneous events were also chosen to further investigate specific features in thunderstorm development. In each case moisture and convective instability were sufficiently available; therefore the convergence was the most important component determining the convective initiation.