By Boltwatch ·
How to Read a Lightning Map: Colours, Time and Distance
Start with your location, the time window and the data source. Together, they tell you what a lightning map is showing. Boltwatch plots reported lightning that has reached the map, so the newest dot is an observation, not a forecast of the next flash.
Check lightning near you1. Choose the place you want to check
Open the live map and tap Near me to measure from your location. Your browser asks for location access. If you prefer to browse a place, open a country, region or city map and zoom to the area you want. A city page initially measures distances from the city centre, which can be some distance from your home.
Look beyond the nearest dot. Zoom out to see whether it belongs to a larger patch of recent activity. Then zoom back in to read the nearby distance and direction. Changing your map view helps you follow the wider storm, but a satellite dot cannot identify the particular street or building that was hit.
2. Read colours as flash age
Boltwatch uses colour to show how long ago a reported flash happened. Newer flashes appear white or pale yellow. Older flashes pass through orange and red, with purple for older activity in a longer window. The age legend explains the scale. Colour is not a measurement of danger, ground impact or the amount of rain.
Choose 15 minutes for a shorter view of recent reports, or 30 minutes, one hour or three hours for more context. A longer window can show a trail of earlier activity after a storm has moved. Switching windows changes which reports are visible; it does not make the underlying data arrive sooner.
3. Check the source and its delay
NOAA GOES-East and GOES-West provide satellite observations over the Americas and adjacent oceans. EUMETSAT Meteosat provides satellite observations over Europe, Africa and surrounding regions. FMI supplies ground-network reports across the Nordics and Baltics. Open map settings to check which sources are selected, and tap a dot to inspect its source.
GOES reports usually reach Boltwatch about a minute after detection. Meteosat reports arrive in ten-minute products, with delivery time on top. A flash near the start of a batch can therefore be older than ten minutes when it first appears. Read the displayed delay and source information before comparing two areas; an outage or slow source can leave gaps.
4. Treat distance and trend as observations
The nearby panel looks for reports within 100 km during the last 30 minutes of the map's display time, using your selected sources. Its nearest distance and direction use that fixed range and period, even when you change the map's visible time window. Closer and Farther compare recent flash distances; they do not give a storm arrival time. A new flash can develop away from the previous cluster, so the nearest report is a description of received data rather than a boundary around all lightning.
For example, a three-hour window may show older red dots beside a town and newer pale dots farther east. That pattern suggests where recent reported activity has occurred. It does not prove that all lightning near the town has stopped. Use a shorter window to inspect the newest reports, while keeping the source delay in mind.
5. Check official warnings alongside the map
Lightning observations, rain radar, forecasts and weather warnings answer different questions. Use your local weather service for expected hazards and advice. An empty map can reflect no reports, a short time window, missing coverage or delayed data. It cannot give an all-clear for outdoor activity.
The US National Weather Service advises going indoors when thunder is audible and waiting at least 30 minutes after the last lightning or thunder before returning outside. Follow your local weather service's guidance. Boltwatch is free to open, with no sign-up needed to view the map.
Frequently asked questions
- Do lightning map colours show how strong a strike was?
- On Boltwatch, colours show flash age. They do not show danger, rainfall or whether the lightning hit the ground.
- Does Near me use the city centre?
- Near me uses your location after you allow browser location access. A city map initially measures from its city centre until you choose your own position.
- Why do more dots appear in a three-hour window?
- The longer window includes older reports as well as recent ones. It does not mean that every visible flash happened just now.