Storm analysis / Largest hail, last hour

Hail track, live radar analysis

Over Winfield, Tennessee, where the map opens. The whole country

The largest hail of the last hour at each place, in inches across: the path each hail storm has cut. How to read it.

Hail track 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 hail track map shows

The largest hail at each place in the hour to each frame, in inches across: the swath each hail storm has cut across the ground. Played, the tracks draw out behind the storms as they move, the widest and longest under the strongest storms.

How to read it

Under 0.75 in: Small hail.
0.75 to 1 in: Penny to quarter.
1 to 1.75 in: Severe hail.
1.75 to 2.75 in: Golf ball to baseball.
Over 2.75 in: Giant hail.

What it is for

Find where hail has fallen, street by street, after a storm passes.
Check a car, a roof or a crop for damage, and when it was likely done.
Follow a hail storm’s path and the direction it is moving.

How it is made

The storm analysis joins every radar in the national network every two minutes into one picture of the country on a grid about two thirds of a mile across, cleaned of ground clutter, birds and insects, and measures from it what no single radar shows: the largest hail, the turning of the wind, how high a storm’s heavy echo reaches above the freezing level, and what is falling, read with the temperature of the air. Storm Station keeps it every ten minutes for a day, the gauged rain and the radars’ view each hour, and draws it at every zoom from the analysis’s own grid.

A frame every 10 minutes, played as a loop of 1 to 24 hours. As data: /radar/now.json?show=meshtrack, the times of its frames.