A mystifying formation over Boulder

Thin, wispy cloud above FL4.Peggy LeMone (NESL/MMM) has always loved clouds. A particularly striking one on the afternoon of March 23 prompted her to write a blog post and carry out follow-up work that could include a peer-reviewed paper.

In her March 30 post at NCAR & UCAR Currents, “A cloud to remember—and a mystery to solve,” Peggy recalls the moment she left FL3 a week before. “I was stopped in my tracks by an incredible sky: a high, very thin layer of small, uniform, tiny cloudlets.” The cloud came and went in about an hour’s time, during which UCAR photographer Carlye Calvin snapped this photo.

In the cloud’s wake came a flurry of discussion among Peggy and weather-watching colleagues. One of the main questions was the cloud’s height. To the naked eye, it resembled cirrocumulus—high, thin sheets of ice crystals—but other clues suggested that it was actually a lower-altitude cloud made of water droplets. The cloud’s thinness made it difficult to determine its height from satellite data. After posting her blog, Peggy continued to dig. She’s corresponded with colleagues that include Tom Schlatter (NOAA) and gathered pilot reports and other data. “I’m pretty convinced now that the cloud is high—which was my first impression,” she says. “This makes this cloud particularly exciting from a scientific point of view. If this is confirmed, the cloud’s height and behavior will challenge the microphysics community.”

At press time, Peggy was working on a follow-up post for Currents, and she and her cloud-watching colleagues may pursue a journal article as well.