May 22 - July 31
Using Radar Attributes and Environmental Parameters to Classify Downbursts Based on Outflow Boundary Speed
Ryan Tatasciore, James LaDue, Lexy Elizalde-Garcia, Melissa Lamkin, Chris Spannagle, Stephanie Edwards, Alyssa Bates, and Samantha Boyd
What is already known:
- The damage potential to lives and property from straight-line, non-tornadic winds
- The dynamical and microphysical processes that lead to downburst formation and intensification
- Near-storm environmental parameters and radar attributes that favor severe winds from downbursts
- The inherent bias on depending on storm reports for the accurate detection and categorization of severe downbursts
What this study adds:
- The usability of outflow boundary (gust-front) speed as a proxy for severe downbursts
- Environmental parameters and radar attributes that correlate well with downburst intensity using a dataset with a large ratio of non-severe cases
- An evaluation of the performance of composite environmental parameters with respect to discriminating between strong and weak downbursts
Abstract:
Downbursts are especially strong, localized downdrafts within thunderstorms capable of producing damaging straight-line winds at the surface. Despite a moderate understanding of the microphysical and dynamical processes that cause downbursts, forecasting and nowcasting their winds remains challenging for National Weather Service (NWS) forecasters. Wind is more sensitive to radar issues and is often difficult to identify compared to other signatures, such as tornadoes. This paper identifies several important environmental parameters and radar attributes that can distinguish the intensities of 47 downburst-producing storms. A focus was placed on pulse storms, mainly in the Southeastern US, as they are more difficult to forecast when compared to more organized modes, such as supercells or squall lines. Using outflow boundary speed as a proxy for downburst intensity, we found a few variables with statistically significant correlation, including total totals, shear parameters, LFC height, and more. There was a poor correlation between boundary speed and more complex parameters that account for wind speed, such as the wind damage parameter (WNDG) and microburst composite (MBURST). These likely performed poorly due to the large number of null (sub-severe) cases in our dataset, as they are designed to identify severe wind potential. Radar attributes — including maximum Specific Differential Phase (KDP) values and maximum 50 dBZ heights above radar level — performed very well, further giving credit to their usability in nowcasting. We found that boundary speed can be utilized as an indicator of downburst intensity, as well as identified significant predictors that can be used to nowcast downbursts associated with pulse storms. Predictor variables we found to be statistically significant were similar to those of previous research that used wind reports as indicators of downburst strength. This research demonstrates the skill of using boundary speed to represent wind intensity, potentially reducing the need to rely on potentially biased storm reports in future work.