Terrain Effects on Frontogenesis and Snowfall Across the Southern Appalachians

Mountainous and complex terrain can have effects on atmospheric flow, the forward speed, and gradients of low-level fronts across the Southern Appalachians. It is theorized that this blocked flow contributed to an enhanced thermal and pressure gradient across the Tennessee Valley and Southern Appalachians on January 29, 2019 resulting in an increase in boundary layer frontogenesis and a band of relatively intense short-duration snowfall that morning. An arctic cold front quickly moved through Eastern Tennessee dropping temperatures nearly 20 degrees in one hour. The morning sounding from NWS Nashville (OHX), the closest proxy site to East Tennessee, observed the well-mixed post-frontal cold airmass extending to around 875mb, above which there was a strong inversion. The depth of this airmass is lower than much of the Southern Appalachians, which can extend up to 2 km in elevation.

Behind the cold front, northwest flow continued to advect colder air into the region as the mountains along the Tennessee and North Carolina border impeded the advancing surface front. The RAP model analysis indicated an increase in the potential temperature gradient, and therefore, an increase in 1000 to 850mb layer frontogenesis. The majority of the synoptic lift and upper-level dynamics lagged several hours behind the event which indicates mesoscale factors more likely contributed to the precipitation band. This study investigates the role terrain played in this strengthening low-level frontogenesis, and its role in producing deep lift in the immediate post-frontal environment yielding significant snow rates across the western foothills of Eastern Tennessee. In addition, this study investigates atmospheric variables in numerical weather prediction that would aid the operational forecaster in identifying terrain induced snowfall events. The identification of such features can greatly enhance operational decision support services to affected communities.