Storm Chamber · Datascape

Radar data

NOAA NEXRAD Level II, file KDDC20130519_000455_V06, from the NOAA Open Data Dissemination archive on AWS (bucket unidata-nexrad-level2). Public domain.

What is drawn

Reflectivity, in dBZ: how strongly the pulse came back from raindrops, hail and snow. It is not cloud. Cloud droplets are too small for this radar, so the real cloud reached beyond what is shown. Echoes weaker than 10 dBZ are left out.

Quality control

Gates whose correlation coefficient (ρhv) is below 0.8 are treated as non-weather (ground clutter, insects, birds) and removed, unless they are 40 dBZ or stronger. Small isolated patches are removed too.

The chamber

An 80 × 80 km box, 20 km tall, gridded at 0.5 km. Each point takes the nearest gate of the sweeps just above and below it, interpolated in dBZ; nothing between the cones was measured. Below the lowest beam and above the highest sweep that reaches a point, the box is empty. A light smoothing removes stair steps.

Light

In the 3D view the reflectivity is shaded as if it were smoke, lit by the sun from where it stood at 7:05 p.m.: west-northwest, 17° above the horizon. The shading is a rendering choice, not a photograph.

Scale and ground

Heights are drawn twice their true size until you switch to true scale. The height ruler always gives true kilometers above sea level. The ground is drawn flat at 653 m, its elevation where the tornado touched down. The radar antenna stands at 813 m.

Tornado

NOAA NCEI Storm Events Database, event 457695: EF4, on the ground from 7:18 to 7:47 p.m. CDT, 7 miles long, up to 1,100 yards wide, no injuries. The dashed line joins the surveyed start and end points; the real path curved north near its end.