Rain rate, live radar

What the rain rate map shows

How hard it is raining or snowing at this moment, in inches of water an hour. Under 0.1 inch an hour is light rain; over 0.3 is heavy; an inch an hour is a downpour that can flood streets.

How to read it

Under 0.1 in an hour

Light rain or snow.

0.1 to 0.3 in

Moderate rain.

0.3 to 1 in

Heavy rain; gutters and ditches fill.

Over 1 in an hour

A downpour that floods streets and underpasses.

Over 2 in an hour

Flash flooding likely, above all in cities and on burn scars.

What it is for

• Time the heaviest rain at a place, to the minute.
• See where streets and creeks may flood before the water rises.
• Read the water in falling snow, which decides how heavy and wet it lies.

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 2 minutes, played as a loop of 1 to 24 hours. As data: /radar/now.json?show=rate, the times of its frames.