The first sign was a major anvil cloud, dozens of miles long, building to the west. We noted the portents, checked NOAA radar via iPhone, and sought shelter at a rest area at Lake Mills, Iowa, where we saw this shelf cloud:
After waiting in the concrete building for the chilly winds behind the front to blow over (literally ... the gusts toppled newspaper stands at our location and knocked down trees elsewhere) we continued north and angled for lightning photos on the way as the front moved east.
I used exposures of two to three seconds, aiming out the passenger window. Such photos tend to be blurry, like this image of phantom trees on phantom hills:
One good thing about time exposures from a moving, handheld camera is that multiple bolts -- leaders and return strokes -- can be imaged separately in the same picture, even though they follow the same ionized channel in the atmosphere. Check out the bolt on the left: it's composed of at least four baby bolts.
Next is an illustration of how a single lightning blast can act like a big flashbulb. Note how the fence posts and grasses are sharp and clear, though it was pitch dark. With our car moving at sixty miles an hour, any normal lighting would have blurred the scene. Observers at the predawn Trinity atomic test at Alamogordo, NM, in 1945 noted the same phenomenon at ignition: for a split second, one said later, he felt he could see every tree and rock for miles.
We got off at an exit to catch this bolt-lit sheet of clouds:
Finally, here's a cloud-to-cloud bolt, spanning 40 degrees of sky.