Diabatic Heating's Influences on the Dynamics of Two Types of Extreme Precipitation Events in the Northeast U.S.

Two Northeast US extreme precipitation patterns from Agel et al. (2017) [Agel, L., M. Barlow, F. Colby, H. Binder, J. L. Catto, A. Hoell, and J. Cohen, 2019: Dynamical analysis of extreme precipitation in the US northeast based on large-scale meteorological patterns. Climate Dyn., 52, 1739–1760], (patterns C3 and C6) are analyzed using the WRF-ARW model with and without diabatic heating, to investigate the role of diabatic heating in the extreme nature of the precipitation in these cases. These two patterns exhibit high values of moisture and moisture transport occurring in conjunction with a warm conveyor belt, in the context of an extratropical storm.

The WRF-ARW model was run using NCEP GFS-FNL data for 20 events (10 from C3 and 10 from C6) from 2000-2008 on both a 36 km and 9 km nested grid from 30N to 50 N and -90W to -60W. Four runs were performed on each event, two runs with no changes made to the model and two runs with all latent heating parameters set to zero. For both control and modified runs, there were two sets of experiments: one initialized 2 days prior to the event, and another initialized 1 day prior to the event. This allowed us to test both the influences of diabatic heating on the extreme precipitation and the formation of the event itself.

In both patterns, removing the diabatic heating resulted in a 40-50% decrease in overall precipitation for the event and shifted the axis of heaviest precipitation south and west. Integrated water Vapor Transport (IVT) values were 25% less, frontogenesis was shifted further south, and vertical velocities were 50% less compared to the no change runs. The higher resolution grid produced more accurate results due, while the two day and one day prior runs showed only modest differences in simulating the extreme events.