A few of you spotted these strange clouds in the sky Sunday afternoon as storms bubbled up around our area. It looks like a storm cloud with a rainbow on top!
Chief Meteorologist Marc Weinberg posted, "This is called a iridescent pileus cap. These pileus caps form on the very top of developing storms at times, but if the sun is in the perfect spot, you get this 'rainbow' effect."
We had two factors working together to get this iridescent cap: strong, developing thunderstorms and sunshine. You have to have both or you won't see the iridescent cap.Â
First, the strong thunderstorm. You may have noticed when we have strong thunderstorms they grow tall then suddenly flatten out at the top. We call that "hitting the cap." Based on the moisture, temperature, wind, pressure, etc. in the atmosphere, there is a limit to how tall a cloud can grow. It's basically like it hit a ceiling; once it hits that point it can't grow up anymore so it has to spread out. Occasionally, a storm that is growing quickly and push through that cap and bubble up above it in a small area. That's the cap you see here!
Second, the sunshine. Those caps are thunderstorms aren't uncommon, but it's hard to find a day with storms that strong where sun is still shining down so brightly. The sun shining through the ice crystals and water in the cap at the top of the cloud produces the colors of the rainbow you see in the iridescence.Â
