How to read a live lightning map

01

What do the dots on a lightning map mean?[1]

Each dot is one detected flash with a computed position and timestamp. Colour almost always encodes age, with the brightest or whitest marking the newest strikes and darker shades fading back through the last hour or so.

The position comes from timing, not from anyone seeing the flash. Ground stations record the arrival time of the radio pulse a strike emits, and the difference in arrival times between stations fixes the location. More stations detecting the same flash means a tighter fix.

Because each dot is a discrete event rather than a continuous field, a lightning map looks nothing like radar. There is no smooth blob of colour, just a scatter of points that clusters where the storm's electrical activity is concentrated.

02

How current is the data?[1]

Typically seconds to a couple of minutes. The radio pulse travels at light speed, so the delay is processing and distribution rather than propagation. That makes lightning data considerably fresher than radar, which needs time to complete a scan.

Radar imagery is often several minutes old by the time it reaches a phone, because the dish has to sweep through its elevation angles before a frame is complete. Lightning detection has no equivalent scan cycle: a flash is located as soon as enough stations report it.

That freshness is the main practical reason to keep a lightning map open alongside radar. When a storm is intensifying quickly, the strike scatter updates ahead of the reflectivity picture.

03

What can a lightning map not tell you?[2][1]

It cannot tell you where the next strike will land. Detection is a record of what already happened, and lightning routinely strikes more than 10 miles from a storm's rain. An area with no dots is not a safe area.

The gap between the last dot and your position is the one people misread most. A quiet map during an approaching storm often means the storm has not begun producing detectable cloud-to-ground flashes yet, rather than that it is harmless.

No prediction

Every dot is a past event. Nothing on the map forecasts the next flash

Coverage varies

Detection efficiency drops where ground stations are sparse, so remote regions under-report

Not all flashes are equal

Most networks favour cloud-to-ground detection; intracloud flashes are often missed or shown separately

Position has error

Fixes carry an uncertainty of hundreds of meters to several kilometers depending on station geometry

Not a safety instrument

Public lightning maps are informational. Thunder remains the decision rule

04

How do you judge whether a storm is coming toward you?[2]

Watch successive strikes rather than the current picture. If each new cluster of flashes appears closer than the last, the storm is approaching. Distance to the single nearest strike is noisy; the direction of travel over several minutes is the reliable signal.

A useful habit is to note the nearest strike distance every few minutes and compare. One flash unusually close to you may be an outlier from a storm that is otherwise moving away, and one distant flash does not mean the storm has passed.

Combine that with thunder. If you can hear it, you are within striking distance regardless of what the map shows, and the 30-minute rule applies from the last thunder you heard rather than from the last dot that appeared.