On March 19, 2026, the final day of astronomical winter, a NASA satellite captured a remarkable image of the scene. An NOAA weather briefing explained the setup: low pressure over the Gulf of Alaska combined with high pressure across eastern Russia and northern Alaska. This pattern pushed frigid Arctic air southeastward across the Alaska Peninsula.

How Cloud Streets Form Over the Ocean

As this cold, dry air flowed over the relatively warmer waters of the gulf, it began to transform. The result was the formation of "cloud streets," long, parallel bands of clouds aligned with the wind. These features develop when the air picks up heat and moisture from the ocean surface. Rising pockets of warmer, moist air create clouds, while cooler air sinks in between, leaving clear gaps.

Closer to shore, the sky remained mostly clear because the air had not yet absorbed enough heat and moisture to form clouds. (Note that the hazy area close to shore might be stratus or sea fog.) Farther offshore, the cloud streets became more defined and gradually evolved into open-cell clouds. These formations appear as thin cloud walls surrounding empty, circular spaces.

Swirling Vortices and Island Effects

Another eye-catching pattern appeared near Unimak Island, the easternmost of the Aleutian Islands. On the island's downwind side, the satellite captured von Kármán vortex streets, which look like repeating swirls spinning in opposite directions. These patterns form when strong winds are forced around elevated terrain, such as islands rising from the ocean.

A Powerful Polar Low Spins Offshore

One of the most dramatic features in the image was a large swirling cloud system about 180 miles (300 kilometers) southwest of Anchorage. Meteorologist Matthew Cappucci identified it as a polar low, a compact storm that develops when cold polar air moves over warmer water. In this case, the system reached tropical storm-force winds and generated snow and even thunderstorms near its center.

A Cold, Stormy Month With More to Come

The striking conditions seen on March 19 were part of a broader pattern. Throughout the month, Alaska experienced persistent cold along with repeated bursts of stormy weather. By late April, temperatures had begun to rise, but reports indicated that unsettled, wet conditions were still on the way for Southcentral and Southeast Alaska as an atmospheric river approached.

NASA Earth Observatory image by Michala Garrison, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview.