When an astronaut aboard the International Space Station snapped this photograph of Lago Argentino in Patagonia on December 27, 2025, a school of fish-shaped clouds lingered over the glacial lake’s teal waters. Determining the clouds’ type and origin from the photograph alone is challenging, but several NASA scientists and university researchers offered a theory after reviewing the image.
“The lens shape reminds me of lenticular clouds, which usually form near or over mountains,” said Maria Hakuba, a research scientist in the aerosols and clouds group at NASA’s Jet Propulsion Laboratory. “The edges of the cloud also look quite smooth rather than ‘fuzzy,’ which suggests they’re ice clouds that are relatively high up.”
Lenticular clouds form as a result of lee waves, which develop when prevailing winds are forced up and over a topographic barrier, often a mountain range, and when the overlying air is stable. Air expands and cools at the crest of the waves, causing vapor to condense and form cloud droplets. Conversely, air on the other side of the waves descends, warming the air and causing the cloud to evaporate. The result is a set of seemingly stationary clouds that hover in place downwind of mountains. Lenticular clouds are often eye-catching, sometimes described as having shapes like almonds, upside-down dinner plates, lentils, flying saucers, or stacks of pancakes.
Hazem Mahmoud, an atmospheric science lead at NASA’s Langley Research Center, agreed that the clouds were likely lenticular and offered additional insight. MODIS (Moderate Resolution Spectroradiometer) data suggest cloud-top altitudes near 9,200 meters (30,000 feet) and cloud-top temperatures around 220 Kelvin, along with relatively large particle sizes consistent with the presence of ice crystals, he said. “The high altitude and microphysical prope …