Wednesday, May 9, 2007

Strange, Unusual Clouds I Still Remember

A year ago today, Orangeblossom (my youngest daughter), her friend, and I were coming home around 7:30pm after a cold front moved through our area. It had been a fairly nice, warm day and rained a bit but there hadn't been any severe weather. The sky looked really different but I couldn't figure out why other than the clouds looked very low and seemed to be reflecting light in a way I had never seen before. Looking closer the clouds seemed to be drooping pendants, hanging very low to us ready to fall on us. I still remember them because they were so unusual.

They seemed very threatening, but I've learned that they are good indicators of a weakening storm because of all the sinking air required to make them. I didn't have my camera so I couldn't take any pictures. I did an internet search and found out they were Mammatus clouds. The University of Illinois at Urbana-Champaign has this information:
"Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air. Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed. As updrafts carry precipitation enriched air to the cloud top, upward momentum is lost and the air begins to spread out horizontally, becoming a part of the anvil cloud. Because of its high concentration of precipitation particles (ice crystals and water droplets), the saturated air is heavier than the surrounding air and sinks back towards the earth. The temperature of the subsiding air increases as it descends. However, since heat energy is required to melt and evaporate the precipitation particles contained within the sinking air, the warming produced by the sinking motion is quickly used up in the evaporation of precipitation particles. If more energy is required for evaporation than is generated by the subsidence, the sinking air will be cooler than its surroundings and will continue to sink downward. The subsiding air eventually appears below the cloud base as rounded pouch-like structures called mammatus clouds. "
More photos from University of Nebraska-Lincoln High Plains Regional Climate Center.

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