Can lightning strike when it is not raining?

01

How far from a storm can lightning strike?[1]

More than 10 miles from the rain. The National Weather Service uses that figure precisely because strikes at that range are common enough to shape the safety advice, and they land in areas where nobody thinks a storm is present.

The mechanism is the anvil. A mature thunderstorm spreads a wide sheet of ice cloud downwind at high altitude, extending far beyond the rain below. Charge accumulates in that anvil, and a discharge from it can travel horizontally before turning down to ground.

From underneath, an anvil is thin, high and often not obviously threatening, particularly if the parent storm is below the horizon. The flash then appears to come from nowhere, which is where the name comes from.

02

Why are these strikes so dangerous?[1][2]

Because they hit people who have no reason to be sheltering. There is no rain, no wind, often no visible storm and nothing to prompt anyone to move indoors, so the strike arrives into a fully exposed population.

This is a large part of why most lightning deaths occur before or after a storm's peak rather than during it. The dangerous windows are the ones that feel safe: the approach, when the storm is still over the horizon, and the departure, when the rain has stopped.

It is also why the 30-minute rule ends up feeling excessive. It is calibrated for exactly this behaviour, and the times it feels most unnecessary are the times it is doing the most work.

03

Is heat lightning the same thing?[3]

Not quite. Heat lightning is ordinary lightning from a storm too far away for its thunder to carry, usually beyond 15 miles or so. A bolt from the blue does reach the ground near you. One is a distant flash you can see, the other is a strike that arrives.

Both correct the same misconception, that a clear sky overhead means no lightning risk. Heat lightning tells you a storm exists somewhere over the horizon. A bolt from the blue tells you its reach extends further than its rain.

04

What should you do under clear sky near a storm?[1]

Use thunder, not sight. If you can hear thunder at all, you are within striking distance and should be indoors. The absence of rain, wind or visible cloud overhead does not change that.

Watching a live strike map helps here in a way that looking at the sky does not, because it shows where flashes are actually landing rather than where the weather looks bad. A storm 15 miles away throwing strikes toward you is visible in the data and invisible from the ground.