If you hear thunder, go indoors. Do not wait for a map marker or distance calculation. Follow official National Weather Service warnings and local emergency instructions.
What the ball markers mean
Each outlined ball marks a recent flash observed by a Geostationary Lightning Mapper aboard NOAA's GOES satellites. A marker can represent in-cloud, cloud-to-cloud, or cloud-to-ground lightning. Its position is an approximate satellite observation and should not be treated as the exact place where lightning contacted the ground.
Marker size and opacity also fade with age, so the newest activity is easier to see without depending on color alone. Dark outlines keep the markers visible over light and dark maps and over colorful radar echoes.
Why lightning colors differ from radar colors
Radar commonly uses green, yellow, orange, and red for precipitation intensity. MyUSA reserves red, orange, and yellow for the distance rings and uses white, cyan, violet, and gray for observation age. This reduces confusion when radar and lightning are displayed together.
Understanding the distance rings
| Ring | Meaning | What to remember |
|---|---|---|
| Red · 10 miles | Closest guide ring | Lightning can occur inside this ring and closer than 10 miles. |
| Orange · 20 miles | Middle guide ring | Shows approaching or nearby electrical activity. |
| Yellow · 30 miles | Outer guide ring | Provides broader awareness around the selected location. |
The rings are centered on the location selected in MyUSA. They are approximate map guides, not boundaries of satellite coverage and not a guarantee of safety outside a ring.
Closest lightning and activity trend
MyUSA calculates the straight-line distance from the selected location to the closest recent satellite observation and shows its approximate age. “Increasing,” “steady,” and “decreasing” compare observations inside 30 miles during the latest five minutes with the five minutes before. “Quiet” means neither period contains an observation inside 30 miles. These trends describe observed activity; they are not forecasts.
Density shading
A soft cyan-to-violet glow appears where many observations overlap. The brighter the glow, the greater the recent lightning density. It helps reveal active thunderstorm cores without claiming that every illuminated point is a separate ground strike.
Where the information comes from
MyUSA combines NOAA GOES-19, which serves the eastern view, and GOES-18, which serves the western view. Overlapping observations are deduplicated when possible. The source is NOAA GOES GLM Level-2 Lightning Cluster- Filter Algorithm data made available through NOAA's Open Data Dissemination Program.
MyUSA is independent and is not affiliated with or endorsed by NOAA or the National Weather Service. The lightning layer supplements official warnings; it does not replace them.
Updates, delays, and outages
The source is checked every five minutes and the map refreshes automatically. Processing, internet delivery, satellite maintenance, or provider outages can delay observations. MyUSA checks the feed time and each satellite's status. When current data cannot be verified, the site says that lightning data is delayed instead of reporting an empty area as having no lightning. Radar remains available independently.
What MyUSA Lightning cannot tell you
- It cannot confirm an exact ground-strike address or structure.
- It cannot reliably separate every cloud-to-ground flash from in-cloud lightning.
- It cannot guarantee that an area is safe because no marker appears.
- It is not certified evidence for insurance, damage, or legal claims.
- It is not an official warning or a prediction of the next flash.
Why another weather app may look different
Some services use paid ground-based detection networks, different update windows, or proprietary grouping methods. MyUSA uses free NOAA total- lightning satellite data. Counts and marker positions therefore may not match apps that advertise exact or ground-based strikes.
Location and privacy
Distance calculations use the location you select or authorize. MyUSA requests only the nearby observations needed for the displayed map and does not use lightning information to track an individual person.
Lightning safety
When thunder is heard, move to a substantial building or hard-topped vehicle. Stay away from windows, plumbing, corded electrical equipment, open fields, isolated trees, water, and metal objects. Remain sheltered for at least 30 minutes after the last thunder. Keep Wireless Emergency Alerts enabled and use more than one way to receive warnings.
Return to MyUSA radar → Official NWS lightning safety ↗ About NOAA GLM ↗
Page reviewed: September 3, 2026