NASA scientists studying fire-driven clouds captured rare imagery of a pileus cloud forming atop a pyrocumulus plume during the Sand Creek fire in Montana.

During an August 11, 2026, flight over Montana's Sand Creek fire, researchers with NASA’s INSPYRE campaign observed a rare pileus cloud hovering above a pyrocumulus cloud. The observation was made using the MASTER instrument aboard a NASA ER-2 high-altitude research aircraft. This event provided scientists with a detailed look at the interaction between intense fire-driven convection and atmospheric moisture.

Formation of the Fire-Driven Cloud

Pileus clouds, named from the Latin word for "cap," typically form when rising air columns collide with a moist layer of air aloft. In this instance, the intense heat from the Sand Creek fire created a fast-rising updraft that displaced a horizontal layer of moister air upward. As this air was forced higher, it cooled and condensed into the veil-like cloud structure. Neil Lareau, the project's deputy investigator, noted that the pyrocumulus cloud acted similarly to a mountain, forcing the air upward to create the cap.

Data Collection and Analysis

The MASTER (MODIS/ASTER Airborne Simulator) instrument captured the imagery at 5:40 p.m. local time. The data included both natural-color images and shortwave-infrared observations, which allowed researchers to map the fire's surface behavior alongside the convective plume. Because pileus clouds are ephemeral and often persist for only a few minutes, the team was fortunate to capture the formation during their 30-minute observation intervals. The imagery provides insight into the extreme updraft dynamics occurring as the fire spread up the western side of Mount Comet.

Broader Context of Convective Clouds

While fire-driven convection is a known phenomenon, pileus clouds can also be triggered by severe thunderstorms or volcanic eruptions. Previous research, such as the 2002 CRYSTAL-FACE campaign in Honduras, documented similar cloud structures above thunderstorms. The INSPYRE mission aims to better understand these processes by connecting surface fire dynamics to the development of convective plumes and cloud structures in the atmosphere.