The Weather Notebook: Skinny Rainbow

Skinny Rainbow
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Photo: Randy Wang
Hi, I'm Dave Thurlow and this is The Weather Notebook. Today we have a listener question that's really two questions in one:

"Hi, my name is Ron Heiss and I listen to The Weather Notebook on WBFO, 88.7 in Buffalo. My question is why are some rainbows wide and other rainbows skinny and how come sometimes there are double rainbows?"

First of all, rainbows that occur in the mid-morning or mid-afternoon tend to be wider than rainbows that occur towards sunrise or sunset. When rainbows appear at these times of day they are closer than they would be at dawn or dusk, meaning that the drops of water that the sunlight bounces around in before it colorfully reflects back to you reflects back to you, are literally closer than they would be in a rainbow at dusk or dawn when the sun is on the horizon. It's closer so it looks wider.

Also notice that these wider rainbows are less then a half circle, the closer to noon it is the flatter the rainbows get. And at noon, rainbows can not be seen from the ground.

In a double rainbow the outside ring, called the secondary rainbow is the mirror image of the inside ring or primary rainbow. The secondary rainbow's light simply comes from the bottom of the raindrops, the primary, from the top. Because raindrops are kinda warped on the bottom as they fall, secondary rainbows only come from tiny raindrops that don't fall as fast. So, if it's raining hard, only look for one rainbow, but if it's just misting I the sunlight you might see two or even three rainbows at once.