Patterns Associated with Cold Season Severe Weather and Tornado Events

There were several significant severe weather events during the winter of 2016-2017. During each of these events the large scale pattern, as diagnosed using Climate Forecast System Reanalysis (CFSR), showed a deep trough to the west and deep warm moist southerly flow over the affected region. These severe weather events had above normal temperatures, precipitable water, and stronger than normal low-level southerly flow.

To put the severe weather events of the winter of 2016-2017 in context, the Storm Prediction Center (SPC) severe weather database from 1950-2017 was analyzed. It was determined that there are some long term trends in weak tornadoes but no significant trends in tornadoes of EF2 or greater intensity. The data was examined for the winter months (DJF) and for a longer cold season which spanned November through March.

Finally, Weather Surveillance Radar, 1988, Doppler (WSR-88D) imagery was used to survey and classify the biggest northern tornado outbreaks during the 2016-2017 cold season. Most of the tornadoes were associated with Quasi-linear Convective Systems (QLCS); however, there were some supercell and embedded supercell tornadoes. The stronger tornadoes and those associated tornadic debris signatures were mostly supercell storms. These findings will aid in forecasting future cold season severe weather and tornado events and work toward our goal of a Weather Ready Nation.