Glossary

Azimuth: Compass direction from the radar to a target.

Azimuthal shear: A derived product highlighting rotation, computed from the change in radial velocity across azimuth. High values mark strong rotation. See Azimuthal Shear.

Base velocity: Radial velocity as measured, including the storm’s overall motion. Contrast storm-relative velocity.

Bounded weak echo region (BWER): A notch of low reflectivity aloft caused by an updraft strong enough to loft precipitation before it falls; a sign of a strong, organized updraft.

Bow echo: A line of storms bulging outward, associated with damaging straight-line winds.

Bright band: A ring of enhanced reflectivity at the melting layer, where snow turns to rain.

Composite reflectivity: The maximum reflectivity across all elevation angles at each point.

Correlation coefficient (CC, ρ_hv): A dual-pol measure (0–1) of how uniform the targets are. Very low CC indicates non-meteorological targets or tornado debris.

dBZ: Decibels of radar reflectivity factor; the logarithmic unit for reflectivity.

Dealiasing: Correcting velocity aliasing to recover true wind speeds beyond the Nyquist velocity.

Differential reflectivity (ZDR): A dual-pol measure of target shape (horizontal vs. vertical return).

Dual-polarization (dual-pol): Radar that transmits/receives both horizontal and vertical pulses, revealing target shape and uniformity.

Echo tops: The height of the highest detectable radar echo in a storm.

Elevation angle / tilt: The vertical angle of a radar sweep above the horizon (e.g. 0.5°).

Hook echo: A curl of reflectivity on a supercell’s rear flank wrapping around the mesocyclone; a classic tornado precursor.

Hydrometeor classification (HC): A dual-pol product classifying precipitation type (rain, hail, snow, etc.).

KDP (specific differential phase): A dual-pol product excellent for estimating heavy rainfall rate.

Level 2 / Level 3: Level 2 is high-resolution base radar data (Archive II); Level 3 is the set of processed NIDS products.

Mesocyclone: A persistent rotating updraft within a supercell; shows as a sustained velocity couplet.

MRMS: Multi-Radar/Multi-Sensor; mosaicked products combining many radars.

NEXRAD / WSR-88D: The U.S. network of S-band Doppler weather radars.

Nyquist velocity: The maximum unambiguous velocity a radar can measure; faster winds alias.

Range: Distance from the radar to a target.

Range folding: Misplacement of returns from beyond the maximum unambiguous range; shown as a no-data/“purple” flag.

Reflectivity: The amount of energy scattered back to the radar; proportional to target number and size. See Reflectivity.

SCIT: Storm Cell Identification and Tracking; the basis for storm tracks and attribute markers.

SPC: Storm Prediction Center, source of watches, outlooks, and MCDs.

Storm-relative velocity (SRV): Velocity with the storm’s motion subtracted, making rotation easier to see.

Supercell: A storm with a persistent rotating updraft (mesocyclone); the type most associated with tornadoes and large hail.

TDWR: Terminal Doppler Weather Radar; airport radars with low tilts and small coverage.

TDS (tornado debris signature): Very low CC co-located with a strong velocity couplet and reflectivity hook; radar evidence of lofted debris, confirming a tornado.

Three-body scatter spike: A weak-echo spike behind an intense core, indicating large hail.

TVS (tornado vortex signature): A small, intense velocity couplet indicating concentrated rotation.

Velocity: Motion toward/away from the radar along the beam (radial velocity). See Velocity.

Velocity aliasing: Artificial wrapping of velocities exceeding the Nyquist velocity, producing abrupt color reversals.

VIL (vertically integrated liquid): An estimate of total liquid water in a column; an intensity/hail proxy.

Volume scan: A complete stack of elevation sweeps; one full radar “frame,” taking minutes to build.

Watch / Warning: A watch means conditions are favorable; a warning means the hazard is occurring or imminent. Warnings always take priority.