A Doppler Radar Climatology of Updraft Proxy Characteristics in Supercells

The project concerns the use of weather radar signatures to estimate the size and tilt of an important storm feature, the storm updraft, within severe thunderstorms. The updraft is an area of rapidly rising air that is transported aloft to form clouds and eventually precipitation. The updraft contributes to every hazard that a storm produces, notably large hail and tornadoes. Past work has provided evidence that larger storm updrafts produce stronger tornadoes and larger hail compared to storms with smaller updrafts. In addition, studies have hinted that storm updrafts that are vertically upright, as opposed to tilted, are also more likely to produce tornadoes. Unfortunately, it is difficult to directly observe and measure characteristics of the storm updraft. However, upgrades performed to the U.S. radar network have introduced new options to track features that serve as a proxy for the updraft. In this project, the researchers use the size and tilt of this radar feature as an estimate for those same characteristics in the updraft in more than 100 actual storm cases to better determine how closely linked updraft size and tilt are to tornado and hail occurrence. The researchers also will determine if the weather conditions feeding into the storm are linked to the size and tilt of the updraft. The project objectives ultimately aim to provide forecasters with new tools that may help them alert the public to storms that are about to produce strong tornadoes and/or very large hail. The storm type being studied is the supercell thunderstorm, which generally produces the strongest tornadoes and largest hail. To estimate the size and tilt of supercell updrafts, the researchers use a novel algorithm that automates detection and area of a dual-pol radar signature, the ZDR column, which forms when an updraft lofts rain and small hail above the freezing level. Those data will be used in tandem with traditional radar analyses to identify links between updraft proxy characteristics, the near-storm environment, and hazard production in large numbers of supercell cases. Specifically, this project seeks to (i) determine a firm link between midlevel updraft area, low-level updraft area, and tornado and large hail occurrence, (ii) quantify the degree to which updraft vertical alignment is necessary for tornado production, (iii) the near-storm environmental controls, if they exist, on both updraft size and alignment, and (iv) combine the results from (i) and (ii) with data of another dual-pol radar signature, the ZDR-KDP separation vector, to optimize known predictors of tornado formation and peak tornado intensity for possible operational use. In addition, depending on project results, the ability to accurately assess these characteristics and their potential use in nowcasting of hazardous weather will be explored. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.