Integrating NOAA NEXRAD Spectrum Width, Storm Relative Motion, and Reflectivity with Damage Survey Overlays
Palmer Wilson, a Blue Raster Senior DevOps Engineer, recently used 3D voxel rendering in ArcGIS Pro to analyze NOAA radar data from the Grand Junction, Tennessee tornado on April 3, 2025. This case study shows how integrating volumetric radar layers can help identify and interpret tornadic structures with greater clarity.
Why Voxels?
Voxels, short for "volumetric pixels", are 3D units used to build spatial visualizations. While they originated in early 90s video games, they are now a powerful tool in geospatial analysis. ArcGIS Pro's voxel capabilities let analysts explore vertical and temporal dimensions of weather events like never before.
Visualizing the Hail Core
By isolating high reflectivity values in radar data, we were able to extract and visualize the storm's hail column. These values typically indicate dense hydrometeors such as hail. Layering this volumetric data on top of 2D composite reflectivity gives insight into the size, intensity, and elevation of the hail core.
Identifying Rotation
Next, we filtered the data to display storm-relative motion. This allowed us to detect a rotating column of air, a classic signature of a mesocyclone. In the 3D scene, the hail column aligns vertically with the region of strongest updraft. Surrounding this core, storm-relative velocity data reveals rotation, with inbound and outbound winds clearly circling the hail column.
- Blue = outbound velocity
- Tan = inbound velocity
This rotating motion combined with vertical alignment shows how the updraft lifts hail-forming precipitation into the storm's core, contributing to storm intensification.
Adding Spectrum Width: A Deeper Look into Turbulence
We also visualized Spectrum Width, which measures the variability in wind speed within the radar beam. High values indicate turbulence and shear, which are key components of tornadic activity. Concentrated areas of high spectrum width appeared near the tornado's center, providing further evidence of violent wind motion.
When viewed together with storm-relative motion, these layers validate the presence of a well-developed tornado embedded within the mesocyclone.
Bringing It All Together
By combining hail reflectivity, storm-relative motion, and spectrum width into a single 3D visualization, we captured a dynamic, multi-dimensional view of the tornado-producing storm. Each layer added context:
- Reflectivity highlighted hail formation
- Velocity showed organized rotation
- Spectrum width pinpointed turbulent zones
Together, they told the full story of the storm's structure, strength, and destructive potential.
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