Analysis and Evaluation of the Non-Supercell Tornado Parameter within the WRF Model over the Green Bay Area

The difficulty of detecting and forecasting the development of non-supercell tornadoes (NST) is well documented. The rapid, low level development of NSTs decreases the warning time as they often develop in minutes and can last only a short amount of time. Even though most NSTs are EF0-EF2, they still cause damage. Development of NSTs is often associated with Mesoscale Convective Systems (MCS), compounding detection due to the complex structure. Research for non-supercell tornadoes has been focused on the amount of CAPE, CIN, shear, vorticity, and low-level lapse of non-supercell tornadoes. These five variables were compiled into the Non-Supercell Tornado Parameter (NSTP) created by Dan Baumgardt and currently used by SPC.

The research presented focuses on the evaluation of this parameter using experimental runs of the Weather and Research Forecasting (WRF) model. Here, we study an event from 06 August 2013 that passed through the Green Bay, WI area, between 0400 and 0700 Z and produced 6 tornadoes along the leading edge of a Quasi-Linear Convective System. The evolution and predictability of the event was analyzed by using 6 different WRF simulations with varying moisture parameter schemes at an 18 km scale. With the WRF, the individual components and actual value of the NSTP were evaluated to see how the different moisture physics schemes affected the forecast with the hope that they would aid in a better forecast. These were compared to the model analysis fields obtained from the North American Regional Reanalysis database. From there, the Read/Interpolate/Plot program was used to further evaluate the WRF forecast and further assess the usefulness of the NSTP as a forecast aid.