κεραυνός: the thunderbolt.
Every lightning strike on earth, as it is detected. Open the instrument →
Live strikes from the Blitzortung network, plotted on a world map as they arrive. Strikes land at full white and fade, busy cells burn into the map, and clusters are tracked as storm cells with a heading, a ground speed, and a second ring when their flash rate is climbing.
No account and no key. A small relay holds one connection to Blitzortung and passes the frames on unchanged. It stores nothing and remembers nothing, and everything the page works out from them goes when the tab does.
Open it and watch. If you want to drive it, this is the whole of it:
| Point | The map reads out the place under the pointer, its coordinates, and the strike count for that 1° cell |
| Pick | Click the map, a feed row, or a ranked place to narrow everything to it; click a storm cell to narrow to the cell rather than the country. Click again or press esc to clear |
| Move | Drag to pan, wheel or pinch to zoom in to about 200 km across. The region names along the top of the map jump straight there |
| Rewind | The track along the bottom holds up to the last hour. Drag anywhere on it to set the clock down at that moment; it then runs forward at life size until it catches up and hands back to live |
| Here | Asks the browser for your location (only when pressed), frames the map on it, and reads out how far away the nearest strike is and how long until its thunder. Session only: not stored, not sent anywhere |
| Link | Zoomed in, the address carries the view as #lon/lat/zoom, so a view can be handed to someone |
| Save | Configuration holds two exports: the retained strikes as CSV, and the frame as drawn, rewound or live, as a PNG |
| Hold | The feed stops advancing while the pointer rests on it, and queues arrivals behind |
| Guide | Seven steps that light each control on the running map in turn. Opens itself once on a first visit; g or guide afterwards, esc to skip |
Keys. k key panel · c configuration · g guide · t dark/light ·
esc close a panel, or clear the current selection. With the map focused, +
and - zoom (or spin the globe) and 0 returns to the whole world. The rewind
track takes arrow keys, home and end.
The guide is the way in; the key panel (k) is the reference. The guide runs
on the live map, dimming everything except the control it is talking about and
leaving that control working, so pressing here while it explains here is
the short version of the explanation. It covers the seven things you need
before you can read the map at all, and then stops. The key panel is the full
catalogue: every mark on the map and every figure beside it.
Beside the region presets, showing the setting they are on. These are the ones worth changing while you watch, which is why they are not behind a panel.
| Dial | Stops | |
|---|---|---|
| view | flat · globe | Flat is the whole planet at once, which is what this is mostly for. Globe is the same data on a sphere: half a world at a time, turned by dragging |
| field | off · cloud · rain | What sits behind the map; see below |
| cells | off · ring · track · full | How much a storm cell carries. Ring is the cell and its flash count, track adds where it has been, full adds where it is going and how fast |
| burn | 4m · 20m · 1h | How far back the burn-in reaches. Four minutes is where it is raining lightning now; an hour is where it has been this session |
| Reading | |
|---|---|
| Rate | Strikes a minute over the last 60 seconds, with a trace, and the number of storm cells being tracked. An ↑ counts the cells whose flash rate is climbing sharply |
| Session | Arrivals by the minute for as long as the tab has been open, the hairline at midnight UTC, and the hardest minute of it. Lightning runs on a schedule: the planet fires hardest over land in the afternoon, so the global rate rises and falls about three times a day as Africa, the Americas and Asia come round into the sun. An hour of history cannot show that; a day of it can |
| Link | Median delay from a strike happening to this browser hearing about it, and the median number of detectors used to place recent strikes |
| Reach | How far each strike was heard, split into daylight paths and darkness. The far end should be longer at night: sunlight makes a lossy layer at 60 to 70 km that the signal has to bounce off, and after sunset the reflection moves up to 85 to 90 km, where less is lost at every hop |
| Here | Present once you have pressed here: distance to the nearest strike, and a countdown to its thunder |
| Most active | Places holding the cells still burning right now, not session totals. Click one to narrow the map to it |
| Strike feed | Each arrival as it lands, named. Click a row to narrow to that place |
c opens it. Everything is stored in this browser and nowhere else.
| Group | What it holds |
|---|---|
| Tube | Phosphor (white, green, amber, ice, and the borrowed palettes oil, crimson, demon; dark mode only), contrast, and bloom |
| Layout | Whether the side panel, header and footer are shown at all |
| Screen | Scanlines, refresh sweep, strike shake, detector clicks, thunder |
| Map | Cell bounds, graticule, frontiers, daylight, capitals, detector threads, imager coverage, aurora, how long a strike stays lit |
| Panel | Which of the readings above are drawn |
| Session | The two exports: strikes as CSV, the frame as PNG |
Both sounds are off until asked for, and thunder needs a position before it can do anything: it is the delay between a strike and its sound reaching where you said you are.
Blitzortung is volunteer hardware. Every strike here is a time-of-arrival fix from stations somebody built, powers and hosts, and the instrument will show you which ones heard each discharge: turn on detector threads and each strike throws a line back to every station that helped place it, for under a second.
The shape of that sheaf is how well the strike was placed. A strike caught in a full sheaf was pinned from every side; one wearing a fan was heard from a single direction, and is drawn a little softer for it. Most of what this network sees, it sees from one side: on a typical strike the widest gap in the ring of stations around it runs past 200°.
Nobody publishes where the detectors are. The ones on the map are assembled from the strikes themselves, over about half a minute of listening, which is also why the map has more on it a minute in than it does on arrival.
Infrared reads the top of the storm column from orbit; radar reads what is falling out of the bottom of it from the ground. They are alternatives rather than layers, because where they overlap they are drawing the same storm.
Their footprints are nearly complementary, and that is the interesting half of the choice. Cloud covers the whole planet including every ocean. Rain covers the ground somebody built and maintains a radar network on, and stops, often sharply, at a coastline. So empty means something different on each: on the cloud field it means clear, and on the rain field it means unwatched, which over most of the planet is what it is.
Off by default. It is what MTG's Lightning Imager saw of the same five minutes from orbit, over the third of the planet that dish can see.
It is worth turning on because the two instruments disagree, and the disagreement is the reading. This network listens for radio from the ground, so what it hears depends on where somebody built a detector, and it hears the cloud-to-ground stroke far better than the discharge that stays inside the cloud. The imager photographs the optical flash instead, and does it as well over the middle of the Atlantic as over Berlin. Where both are lit, two unrelated instruments agree there is a storm there. Where the layer is lit and no strikes arrive, the network is deaf rather than the sky quiet, which over central Africa is most of the time.
It runs about fifteen minutes behind the strikes on top of it, because a five-minute accumulation has to close before it can be processed and published. An unlit patch under a firing cell usually means the satellite has not been asked yet.
Off by default. The auroral oval is where the solar wind is being funnelled down the earth's own field lines into the top of the atmosphere, and it is the one layer here that can be on beside everything else without arguing with it: it lives at the latitudes lightning does not, so it cannot cover a reading. Worth turning the globe for, because a sphere shows a whole polar cap at once where a flat map cuts the same ring into two unrecognisable arcs along its edges.
It is also the one thing on this instrument that has not happened yet. Everything else here was measured; this is NOAA's OVATION model, driven by the solar wind as it is read at L1 about an hour upstream of us, which is exactly what buys it the lead time. The panel says how far ahead it is looking.
The curtain shimmers, on a slow wave that runs around the oval rather than pulsing all at once, which is roughly what a substorm does. The shimmer is texture and says nothing: it moves a third of the weight, and where the oval sits and how bright it is are the model's to report. It holds still for anyone who has asked their system for reduced motion.
An hour, if an hour fits. The rewind track is as long as the history actually held: up to 120,000 strikes are retained, so at the quiet end of the world's rate the full hour is comfortable, and at the peak the ceiling binds first and the window is shorter. The track grows as the session runs, and shows what it has rather than what it wishes it had.
Setting the clock down starts it running forward again at life size, rather than freezing a frame: what you want from a map of a storm is to watch the storm move. Three things are not replayed: storm rings, which are tracked forward strike by strike and cannot be rebuilt from a single instant; bolts and the chassis knock, because an event does not happen twice; and nothing is lost behind you, so returning to live finds the present already there.
Capitals are lit by the weather rather than drawn as furniture. A name surfaces when a burning cell is within 400 km of it and fades with the smudge underneath, so a quiet map carries no names at all. Pointing at the map already names whatever is under the cursor, in the corner, on demand.
Everything here comes from a stream nobody archives and is held for an hour in a tab. Closing it loses the hour, which is right for a live map and wrong for the one afternoon the storm was worth keeping.
The CSV is exactly what is retained: flash_utc, received_utc, lon,
lat, one row per strike, nothing reconstructed. The gap between the two times
is the network's own delay, strike by strike. It is the figure the panel only
ever shows you the median of.
The PNG is the frame as drawn, read off the canvas: scrub to the squall and save, and what you get is the squall. It is the one way a moment can be handed to somebody. A link cannot do it: the address carries the view, but the strikes under it belong to this session and cannot travel, so a shared URL opens on the right coordinates with whatever weather happens to be there.
Blitzortung asks that a project using their data take it from its own server rather than from theirs, and it is easy to see why: every open tab used to hold its own connection, so a hundred people watching was a hundred connections to hardware that volunteers buy, power and host.
relay/ is that server. It is a single Cloudflare Durable Object holding one
upstream connection however many people are watching, fanning the frames out
untouched. Nothing is decoded there, nothing is stored, and no strike outlives
the moment it is passed on. The instrument is still built entirely in your own
tab, from a feed that now arrives by way of one socket instead of thousands.
npm install
npm run dev # dev server
npm run build # production build
npm run lint
npm run check # checks the palette, the geometry and the fetched fields against live dataThe page needs a relay to get its strikes from. Deploy one to your own Cloudflare account, or run it locally:
cd relay && npm install
npm run dev # serves ws://localhost:8787/feed
npm run deploy # to your account, once wrangler is logged inThen point the site at it: copy .env.example to .env.local and set
VITE_FEED_URL. Set ALLOWED_ORIGINS in relay/wrangler.jsonc before the
relay is reachable from the internet, or anyone who finds the hostname can use
it and the single-socket property becomes theirs to spend.
No API keys anywhere.
node scripts/KeraunosSeeker.cjs is a standalone Node client that prints the same
stream to the terminal. It connects to Blitzortung directly, so it is a tool for
one person at a terminal rather than something to put behind a website.
The pictures in this file are captured from the running instrument rather than pasted in once, so they can be taken again when it changes:
npm run dev # in another terminal
npm run shots # all of them, into docs/shots and public/og.png
npm run shots -- hero # one
VIEW=-99.4/41.2/6 npm run shots -- hero # framed somewhere elseEach shot soaks before it fires: grabbed on load, the instrument is a black
rectangle and a fair picture of nothing. Pick a VIEW that is firing at the
time of the run (the panel's activity ranking says which), or the hero shows an
empty ocean at three in the morning.
This is an instrument for watching the weather, not for deciding what to do about it. Blitzortung is a volunteer network and says so plainly: the data is for private and entertainment purposes, and explicitly not for storm warning, for checking overvoltage claims, or for risk analysis. It is not for the protection of life or property, and neither is this.
That matters here more than it would on a map of dots, because the instrument will tell you the distance to the nearest strike and count down to its thunder. Those are the two readings most easily mistaken for a safety tool. They are arithmetic on a feed that is incomplete by construction: the network hears the cloud-to-ground stroke far better than the discharge that stays inside a cloud, and it hears nothing at all where nobody has built a detector. A quiet map is not a safe sky.
If you need lightning data to make a decision with, use your national meteorological service.
Strikes from the Blitzortung network and its volunteers, whose data stays under their terms and under CC BY-SA 4.0. The MIT licence on this repository covers the code in it and nothing else: the strikes are not this project's to relicense, and commercial use of them is prohibited by the people who collect them.
Cloud field from RealEarth (SSEC, University
of Wisconsin-Madison) and EUMETSAT; rain field from
RainViewer; imager coverage from EUMETSAT's
MTG-I Lightning Imager; the auroral oval from
NOAA SWPC's OVATION model. The borrowed phosphor
palettes are credited in src/lib/palette.js.