If you hear thunder, move immediately to suitable shelter. Lightning maps can help you understand a storm, but the shelter decision should not wait for a dot to appear near you. This guide explains what thunder and lightning observations mean and how to build an outdoor plan around current National Weather Service guidance.
Choose shelter before you need it
The NWS lightning safety guidance identifies a substantial building with electricity or plumbing, or an enclosed metal-topped vehicle with the windows up, as suitable shelter. Stay sheltered for at least 30 minutes after the last thunder. There is no safe outdoor location when thunderstorms are nearby.
Inside, avoid plumbing and direct contact with electrical equipment; stay away from windows, doors and porches. An isolated tree, tent or open shelter is not an adequate substitute. If you are responsible for others, decide how everyone can reach suitable shelter before starting an activity.
Review the forecast for the activity's full duration and allow time to move the entire group. A location with a long walk to shelter needs an earlier cancellation or relocation decision. Account for people who move slowly, need assistance or cannot hear thunder; make sure the group has an accessible way to receive the instruction.
Why you hear thunder and see different flashes
Lightning is a rapid electrical discharge involving charged regions in the atmosphere or the ground. The channel heats surrounding air rapidly, creating the sound heard as thunder. A flash can remain within a cloud, pass between clouds or connect to the ground. The National Severe Storms Laboratory lightning FAQ explains these processes and why one flash can include multiple strokes.
The light reaches you before the sound, so a delay between flash and thunder is expected. That delay describes a past discharge; it cannot establish where the next one will occur. Lightning can also extend away from the heaviest rain. The NSSL lightning types guide describes cloud and ground paths and lightning outside the rainy part of a storm.
“Total lightning” combines several types of lightning activity. “Cloud-to-ground lightning” is a narrower category. Compare like measures when reading a map or a claim that lightning activity has increased.
Know what the detection system measures
Ground networks detect electromagnetic signals from discharges; satellite instruments observe optical signals. Their coverage, detection methods and displayed products differ. NOAA's Geostationary Lightning Mapper (GLM) explanation describes continuous observation of total lightning, including in-cloud, cloud-to-cloud and cloud-to-ground activity.
GLM helps forecasters examine storm development alongside radar, other satellite information and surface observations. A satellite flash-extent display describes lightning activity across an area; interpreting every illuminated pixel as a precise ground impact would change the meaning of the product.
| Check | Question | Why it matters |
|---|---|---|
| Detection type | Ground strikes, total flashes, flash extent or another product? | Different products count and locate different aspects of a discharge. |
| Timestamp | When was the latest observation, and in which time zone? | A recently opened screen can show older data. |
| Accumulation window | One instant, several minutes or an hour? | A larger window can contain many earlier flashes. |
| Coverage and legend | What area is observed and what do the symbols mean? | An empty-looking area may reflect display or data limitations. |
Use the map's own documentation and the warning text. A clean patch on a display is insufficient evidence that an outdoor location is safe.
Assign the decision and the message
For an organized outing, name the person who monitors the forecast and initiates the shelter plan. Name a backup. Identify the destination, how participants will be told, the route to shelter and who confirms everyone has arrived. Practice a simple message such as “Move to the designated building now” so the response is familiar.
The OSHA/NOAA outdoor-work lightning guidance describes planning, weather checks and shelter for outdoor work. Apply the relevant workplace or venue procedures when those govern the activity. Recheck the plan if a building is locked or a vehicle is unavailable.
Use observations to learn, and warnings to act
For learning, compare the same storm's radar and lightning products using matched timestamps. Note whether the displayed lightning is total activity or ground contacts, and how the accumulation window changes the picture. This is an observation exercise to do from shelter.
For an immediate threat, follow official warnings and venue instructions. Keep a second way to receive weather information and review the plan before the next activity. The mobile weather guide explains how to check phone alerts and timestamps.