Live radar / Echo tops

Storm tops, live radar

Over Citizen station N7TUG, Washington, where the map opens. The whole country

How tall each storm stands, in feet: the higher the top, the stronger the storm and the more likely hail and wind. How to read it.

Storm tops on the map

The rings are the storms the radars detect, the larger ring a severe one; each line runs to where its storm will be in an hour if it keeps its present speed and heading. Rotation and hail are what the radars detect and the analysis measures, not warnings: the official watches and warnings in force are drawn on the map in their own colours and set out in full under Alerts.

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.