High above Earth, not all clouds are what they seem. While most are natural formations, fluffy white cumulus clouds or ominous thunderstorm-dark cumulonimbus, some peculiar shapes are directly linked to human activity. One such fascinating formation is the fallstreak hole, or what many refer to as a hole-punch cloud.
What Are Hole-Punch Clouds?
Hole-punch clouds are striking circular gaps in mid-level cloud layers, particularly altocumulus. These clouds consist of supercooled water droplets, which are water particles below freezing temperature that remain in liquid form due to the lack of ice crystals.
When ice crystals do form, they grow quickly by absorbing moisture from nearby supercooled droplets, causing those droplets to shrink or evaporate. The result is a circular hole in the cloud, often described as looking like a portal or an atmospheric puncture.
How Do Airplanes Create These Clouds?
According to Andrew Heymsfield of the National Center for Atmospheric Research (NCAR), airplanes are instrumental in triggering these unusual formations. As aircraft pass through clouds, air near their wings and propeller tips expands and cools rapidly due to reduced pressure. This sudden cooling can drop temperatures below the surrounding cloud layer, causing supercooled water droplets to freeze into ice crystals.
These heavier ice crystals then fall, forming a visible gap in the cloud—hence, a fallstreak hole.
Rain and Snow From the Sky
Heymsfield’s research found that this phenomenon not only creates a hole in the sky, but can also produce rain and snow at lower altitudes. When jets fly through humid, mid-level clouds, the freezing process that forms the ice crystals can lead to precipitation—sometimes in the form of snowfall.
The team observed this over Texas, using satellite data from NASA’s CloudSat and weather models from NCAR. Hundreds of these holes were recorded in areas with regular flight activity. Interestingly, it didn’t matter what kind of aircraft—commercial jets, private planes, or military aircraft—all had the same effect on the cloud structure.
Visible From the Ground and the Plane
These dramatic cloud formations aren’t just visible to skywatchers on the ground. Heymsfield explained that passengers aboard airplanes flying through humid regions can often see a faint “veil of clouds” near the wings. That veil is a supercooled cloud beginning to freeze due to air expansion and cooling.
The hole-punch clouds often expand for hours after their initial formation, making them one of the more enduring human-made impacts on the sky.
