Cloud Patterns Signal the End of Winter in Alaska
Explore 7 Q&A about cloud formations over the Gulf of Alaska on March 19, 2026, explaining cloud streets, open-cell clouds, von Kármán vortices, and a polar low.
In March 2026, winter's final days in southern Alaska were marked by dramatic cloud formations off the coast, captured by NASA's Terra satellite. These patterns revealed the atmospheric instability as cold Arctic air surged over warmer ocean waters. Below, we explore the science behind these striking clouds.
What did the NASA satellite capture on March 19, 2026?
On the last day of astronomical winter, NASA's Terra satellite used its MODIS instrument to photograph a stunning array of clouds over the Gulf of Alaska. The image showed cloud streets, open-cell clouds, von Kármán vortex streets, and a polar low. This snapshot came at a time when parts of Alaska were experiencing below-normal temperatures and heavy snow, despite the calendar saying winter was over. The clouds visually captured the clash between cold Arctic air and relatively warm ocean water, a classic sign of winter's end.
Why did the clouds form in such striking patterns?
The formations were caused by a combination of low pressure over the Gulf of Alaska and high pressure over eastern Russia and northern Alaska. This pressure difference funneled frigid, dry Arctic air southeast over the Alaska Peninsula and out over the open sea. As this cold air moved over the comparatively warm Gulf of Alaska waters, it picked up heat and moisture, triggering condensation and cloud formation. The wind direction and ocean temperatures shaped the distinct patterns, from parallel bands to swirling vortices.
What are cloud streets and how did they appear?
Cloud streets are long, parallel bands of clouds that align with the wind direction. In the image, they formed as cold, dry air swept over the warm ocean. Where the air rose, moisture condensed into clouds; where it sank, clear skies appeared. These bands didn't form immediately—the air needed time over the sea to collect heat. That's why the coastal strip appears mostly cloud-free. As the air moved farther offshore, the cloud streets matured into more complex shapes, like open-cell clouds.
How do open-cell clouds differ from cloud streets?
Open-cell clouds look like thin wisps of cloud surrounding empty pockets of clear air. They form when the air mass continues to warm and rise, causing the cloud streets to break apart. In the Gulf of Alaska scene, the air gained enough moisture over distance to transform the parallel bands into these cellular structures. Open-cell clouds are common in regions where cold air flows over warm water, and they often indicate ongoing convection—like tiny thunderstorms. In this case, they marked the transition from simple linear patterns to more chaotic weather.
What are von Kármán vortex streets and where did they appear?
Von Kármán vortex streets are repeating swirls of clouds that form when wind is diverted around a raised obstacle, like an island. In the satellite image, they appeared on the lee side of Unimak Island, the easternmost of the Aleutian Islands. As the strong winds hit the island, they split and spun into counterrotating eddies downstream. These patterns are named after the engineer Theodore von Kármán and were clearly visible as staggered swirls in the bottom-left of the scene. They show how terrain can shape cloud patterns far downwind.
What was the polar low spotted southwest of Anchorage?
About 180 miles southwest of Anchorage, a large cloud vortex caught meteorologists' attention. It was a polar low—a small, intense cyclone that forms in cold polar air over warm water. According to meteorologist Matthew Cappucci, this particular polar low carried tropical storm-force winds and produced snow and thunderstorms near its center. Polar lows are rare and can be dangerous because they develop quickly and bring severe weather. This one highlighted how winter's end can still pack a punch in the Gulf of Alaska.
Why was the area near the coast mostly cloud-free?
The coastal region appears hazy but largely cloud-free because the cold air had just started its journey over the ocean. It takes time for the air to absorb enough heat and moisture to form clouds. Near shore, the air was still too dry and cold to condense. The hazy area might have been stratus clouds or sea fog, but it lacked the defined patterns seen farther out. This clear zone reinforces the process: clouds don't appear instantly, and the distance from land determines their development stage.