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WSR-88D radar at full resolution, live and archived to 1991. Free, without an account or advertising.

Level II data

Most radar sites display Level III: a reduced, smoothed product derived from the original scan and distributed at a fraction of the size. This site displays Level II, the radar's output before that reduction.

The products

The scans below are from KPAH at 0.5° elevation on 11 December 2021, as the Mayfield, Kentucky tornado moved through the town. Reflectivity and velocity are separate passes of the same rotation, seconds apart.

Reflectivity

Power returned by precipitation, in dBZ. Higher values indicate heavier precipitation or larger particles. Values above roughly 60 dBZ generally indicate hail.

Reflectivity from radar KPAH showing a supercell over Mayfield, Kentucky, with a small magenta core of extreme returned power at the town.
Reflectivity, 03:27:50 UTC. The magenta core at Mayfield is a debris ball: material lofted by the tornado, returning more power than the surrounding rain.

Velocity

Motion along the beam, toward or away from the antenna. Adjacent maxima of opposite sign indicate rotation. A tight, intense pair at low elevation is the radar signature of a tornado.

Radar velocity showing strong outbound and inbound returns immediately adjacent to each other over Mayfield, Kentucky.
Velocity, 03:27:50 UTC. Strong outbound motion meets strong inbound motion across a few hundred metres at Mayfield. The two colours touching is the rotation.

Correlation coefficient

How consistently the targets within one sample volume scatter energy. Rain and snow are uniform and read near 1. A sharp, localised drop indicates a mixture of sizes and shapes, most often lofted debris.

Correlation coefficient showing a dark low-value area over Mayfield, Kentucky, against uniformly high values in the surrounding rain.
Correlation coefficient, 03:27:32 UTC. The dark area over Mayfield is where correlation collapses. This is how a tornado on the ground is confirmed from radar alone, at night and without a spotter.

Differential reflectivity

The difference between power returned in the horizontal and vertical polarisations, which indicates the shape of what the beam is hitting. Raindrops flatten as they fall and read positive. Hail has no preferred orientation and reads near zero.

Data sources

All of it is public data. This site decodes it and renders it.

Limitations

This is not a warning service. Radar depicts conditions measured minutes earlier, at an altitude that increases with distance from the antenna. Beyond roughly 100 miles the beam overshoots much of a storm entirely.

For decisions about your safety, follow the National Weather Service and your local emergency management. Warnings appear on the map here as context, not as an issued product.

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