How long after thunder is it safe to go outside?

Why 30 minutes

Storms produce lightning after the rain stops and after the thunder fades, and the trailing part of a storm is where a lot of people are hit. Thirty minutes of silence is long enough for a storm to move well beyond the 8 mile shelter distance. The National Weather Service has used this rule for decades and it is still the rule for anyone without detection data.

Why it is called a last resort

The CISA guide for sports and events says the 30 minute rule is no longer the safest or most accurate method. People mishear thunder, forget to restart the clock, and go back out while the storm is still within range. It works only when you follow it strictly.

The better way, when you have data

With real-time cloud-to-ground and in-cloud detection, resume when all three are true: lightning has moved beyond 8 miles, the storm is carrying it away from you, and nothing new is forming inside 8 miles. Before It Strikes runs this test continuously and shortens its countdown when a storm has clearly left, and holds it when the storm is stalling or rebuilding.

Quick answers

How long after thunder is it safe to go outside?

Thirty minutes after the last thunder or flash, restarting the clock on every new one. With real-time lightning detection you may go out once lightning is beyond 8 miles, moving away, and not redeveloping.

Is the 30 30 rule still valid?

The 30 second part is a distance estimate and the 30 minute wait is still correct without detection data. Official guidance now calls it a last resort because real-time detection is more accurate.

Guidance on this page follows the National Weather Service lightning safety toolkit and the Lightning Safety Guide for Sports and Special Events published by CISA and the National Center for Spectator Sports Safety and Security (May 2026). Official NWS warnings always take precedence.