Lightning Tracker combines NOAA GOES-19 East and GOES-18 West GLM optical-flash feeds for supported portions of United States and Canada maps, and EUMETSAT MTG-I1 LI for the United Kingdom map. Fixed source boundaries prevent overlapping satellite observations from being counted twice.
For what an optical-flash marker can and cannot locate, read how accurate lightning maps are. For counts and rates outside this live detection window, read US lightning statistics.
Each layer answers a different question. Lightning detections are not precipitation radar, and neither replaces an official warning.
NOAA's Geostationary Lightning Mapper instruments detect optical lightning flashes from orbit. Lightning Tracker assigns East and West observations to deterministic longitude bands, split at a -106.1° longitude, so their overlapping views do not produce duplicate flashes in the shared pipeline. This uses NOAA product GLM-L2-LCFA.
EUMETSAT MTG-I1 Lightning Imager supplies recent optical flashes for the United Kingdom regional map and for the European country routes in Polish, French, German, Dutch, Swedish, Italian and Spanish. A second fixed longitude boundary separates its Atlantic overlap from GOES East processing at -37.5° longitude. The UK and European public routes are capped at that boundary. EUMETSAT collection: EO:EUM:DAT:0691.
SPC convective outlooks provide categorical and probabilistic storm-risk context for days 1 through 8. They are forecasts, not live lightning detections, and remain visibly separate from map markers and nearby-strike results.
Neither this site nor a released app build shows a precipitation-radar layer. Radar measures reflected energy from rain, hail and snow; it does not detect lightning, and a lightning detection is not a rainfall measurement. For rainfall, use your national weather service radar. If a future release adds a radar layer, the app's own About screen is the source of truth for the provider active in an installed version.
GLM events are illuminated pixels in a 2 ms frame. Adjacent simultaneous events form groups; groups within less than 330 ms and 16.5 km form flashes. Group and flash locations are radiance-weighted centroids, not surveyed ground-impact points.
Deduplication is deterministic: stable provider event IDs use a shared source + provider_event_id identity, and fixed disjoint longitude bands prevent cross-satellite overlap. These rules remove duplicate pipeline records; they do not create a latency guarantee.
Three clocks affect what appears on screen. A fixed poll interval never guarantees an identical end-to-end delay.
Satellite processors publish products after observation. Availability varies with source processing and network conditions.
Lightning Tracker checks GLM feeds every 30 seconds and MTG LI every 60 seconds, then parses and stores new flashes.
Source filtering, deterministic overlap handling, persistence, clustering, and API delivery add variable processing time.
Public interactive maps request fresh data every 90 seconds while open. A browser can therefore update later than the server poll.
Practical meaning: GLM 30 seconds, MTG LI 60 seconds, and browser 90 seconds are cadences—not promises that every observation appears within that exact time.
GLM and LI observe optical lightning flashes, including substantial intra-cloud activity. Do not interpret every marker as a classified cloud-to-ground strike.
Satellite visibility, source processing, network delivery, and refresh timing can delay or miss detections. If you hear thunder, move indoors.
Public routes exist for the United States, Canada, and the United Kingdom. The GLM pipeline treats coverage as full only through 52°N and as edge coverage from 52°N through 55°N. Alaska and Canadian locations north of 55°N are outside the configured GLM footprint and may return no provider. The UK route uses MTG-I1 LI. Route availability never proves complete detection or all-clear.
Use local meteorological agencies and emergency authorities for official warnings. Lightning Tracker adds situational context; it does not replace them.