An Analysis of Terrain Influences on Ice Events Across WFO Morristown, Tennessee Forecast Area

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Monday, 5 January 2015
Andrew Pritchett, NOAA/NWS, Morristown, TN

An Analysis of Terrain Influences on Ice Events Across WFO Morristown, Tennessee Forecast Area

Andrew Pritchett National Weather Service, Knoxville/Tri-Cities, Tennessee

Winter weather across the southern United States, especially ice events have a huge societal impact due to the lack of resources required to alleviate the issues caused by them. There have been some notable events across WFO Morristown, Tennessee County Warning Area (CWA), such as January 22, 2008, December 16, 2010 and January 24-25, 2013. Though these events produced localized hazardous condition, they had much less of an widespread, lingering impact than in neighboring areas of middle/western Tennessee, Kentucky and Alabama despite model guidance suggesting otherwise. A vast majority of the forecast “misses” occur when the sub-freezing temperatures needs to be advected southeast into the area.

By examining the synoptic and mesoscale conditions from events over the previous 30 years, it has shown that most of the notable ice events occur when subfreezing air is already in place in advance of the precipitation. It is hypothesized that model guidance, even high resolution mesoscale models, fails to account for the terrain blockage along the spine of the Cumberland Mountains.

The Cumberland Mountains and Plateau stretch in a southwest to northeast orientation from east central Tennessee into southwest Virginia near the Kentucky state-line. These terrain features prevent the shallow cold air from pulling south into the Tennessee Valley before the precipitation moves in. As a result, forecasted icing amounts are vastly overestimated in these situations. This study examines the influence of the Cumberland Mountains and Plateau during ice storms events in order to improve the accuracy of winter forecasting across WFO Morristown's CWA.