Weird cloud – Interesting story! (H. Michael Mogil, CCM, CBM, NWA-DS*)
The other morning (10/21/21), marked the end of an early-season cooler and drier weather pattern across southwest Florida. It also marked the return of mid-level moisture to the region (as was evidenced by an extensive layer of altocumulus clouds (Fig. 1). These water-laden, puffy-looking clouds typically occur between 8,000 and 12,000 feet above ground level (roughly two miles high).
Altocumulus clouds can take many forms, but these showed the more common banding pattern. This pattern typifies a wave running perpendicular to the cloud bands. Where the air rises, cooling takes place and clouds form; where the air sinks, the clouds evaporate. Think about up and down patterns you might see as ocean waves approach the shore.
Roughly thirty minutes later, a large part of the altocumulus layer transformed, with a new cloud taking on a feather-like appearance (Fig. 2). This cloud, although still at the altocumulus level (and still surrounded by water-laden clouds) had become an ice-crystal cloud. The cloud-free region in which the transformation took place surrounded the feathery cloud.
The key to this transformation most likely involved (1) the presence of super-cooled water (i.e., water existing at a temperature below 32 degrees Fahrenheit), (2) “seeding” of the altocumulus cloud by ice crystals from above, and/or (3) the passage of an airplane through the cloud (which disrupted the water molecules in the cloud and added water vapor and solid particles to the existing cloud).
Once the transformation to an ice cloud begins, it will continue because water will want to move toward the ice crystals. An hour later, almost all of the altocumulus clouds had been replaced by ice-crystal clouds.
This type of hole-in-the-cloud is sometimes referred to as a “hole-punch” cloud. Often the cirrus-type cloud is located within a nearly circular hole in the altocumulus layer.
I’ve only seen a few of these clouds in my lifetime. However, I recall my first encounter while I was a student at Florida State University. The day was very much like last Thursday and the sighting was also shortly after sunrise. The day was cool, too (temperatures in the 60’s).
The best part of this sighting was that I was able to frame an entire 45-minute Zoom-based talk to a seventh-grade homeschool group in Illinois that Thursday evening. I used the cloud images to discuss the water cycle and phase change processes, create a cloud in a bottle, make it snow, and much more.
The kids loved it because there were “demonstrations/experiments” and things related to a real-life event. Or as one mother quipped afterward, “…understanding weather is important and more complex than the little report on hurricanes in the 4th grade.”
© 2021 H. Michael Mogil
Originally posted 10/25/21
* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.