Storm tops, live radar

What the storm tops map shows

How high each storm reaches, in thousands of feet: the highest the radar still finds rain or hail. Ordinary showers stop near 20,000 ft; a top over 45,000 ft is a towering storm, the kind that brings hail and damaging wind.

How to read it

Under 20,000 ft

Showers and light rain.

20,000 to 35,000 ft

Thunderstorms.

35,000 to 45,000 ft

Strong storms, reaching high into the sky.

Over 45,000 ft

Towering storms that can bring hail and damaging wind.

Over 55,000 ft

The strongest supercells, their tops punching above the anvil.

What it is for

• Tell a shower from a thunderstorm when both look alike on the radar.
• Find the storms growing fastest: a top that climbs quickly is a storm strengthening.
• See which storms an airliner must fly around.

How it is made

Every radar in the national network, more than 150 of them, sweeps the sky every few minutes, tilting up through a set of angles. The sweeps are joined into one picture of the country on a grid about a third of a mile across, each place taking the lowest beam that sees it clearly. Each picture is checked against the national analysis before it is drawn, and echo it does not confirm (birds, insects, ground clutter, the beam bent back to the ground) is left out.

A picture every 5 minutes, played as a loop of the last hour. As data: /radar/now.json?show=tops, the times of its frames.