Mammatus clouds, Hastings, Nebraska

From Twitter today; working to track down more details.

A photo by John C. Olsen, taken in Hastings, Nebraska, perhaps on December 31, 2013:

From Fascinating Pics: One of the rarest weather phenomena, Mammatus Clouds. Photo taken by John C. Olsen in Hastings, NE pic.twitter.com/dlPNaPa25D

Our boys liked clouds from the start.  A couple of our early cloud identification books featured mammatus clouds (guess where the name came from); and before each boy was 11, we had seen these clouds here in Texas, often in that treacherous time known as tornado season.

Beautiful clouds, yes, but often scary — well, until you read from the University of Illinois that they tend to follow nasty storms, not precede them.

Mammatus Cloudssagging pouch-like structuresMammatus 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.

Mammatus are long lived if the sinking air contains large drops and snow crystals since larger particles require greater amounts of energy for evaporation to occur. Over time, the cloud droplets do eventually evaporate and the mammatus dissolve.

Our experience is the clouds look a lot cooler than can be captured on film or in electronic images.  Mr. Olsen captured a great image.

Very nice shot