A rotating cloud in a California storm.

When Angela Walfoort looked up into the Northern California sky the evening of May 24, it looked like an alien invasion was underway.

“It was breathtaking. Awe-inspiring. Truly an amazing experience,” she wrote.

Her photo — since shared thousands of times — captures an incredible shot that many Tornado Alley storm chasers spend years longing for. A towering “LP supercell,” or low-precipitation supercell, is seen spinning like a top through parts of Shasta County south of Redding. As the sun begins to set, the boiling cloud mass is bathed in an amber, peachy light. For about an hour, residents in the Cascade region were treated to an otherworldly scene.

The rotating cloud tower did trigger a tornado warning, with funnel clouds spotted at 8:35 p.m. last Friday. The warning also predicted “two inch hail.” The National Weather Service received “multiple reports of golf-ball to tennis-ball size hail … on the east side of Redding from 8:05 p.m. to 8:20 p.m.” No tornado touched down.

The California storm that spawned the rotating cloud.

A storm this powerful would be impressive even by Oklahoma standards, but to see something like this in California is incredible. Since bookkeeping began in 1950, California has seen only three instances of hail topping 2.5 inches in diameter — placing the Redding cell among the elite.

Walfoort was in Cottonwood when she snapped the picture. Her photo shows the rotating updraft of the storm, where warm air spirals inward and upward, in the foreground. Behind this corkscrew updraft tower is probably a narrow shaft of heavy rain and hail. In the distance, the storm’s pink and violet anvil can be seen spreading outward downwind. From time to time, sheet-light crackles of lightning can crawl along this 10-mile-high anvil.

The height of the California storm.

LP supercells tend to be the most visually stimulating storms since they have little rain obscuring their structure — that’s where the “low precipitation” part comes from. While they can produce all modes of severe weather, LP supercells are often smaller and may mark a phase at the end of a supercell’s life cycle. But don’t be fooled — LP supercells are dangerous; they can, and occasionally do, produce tornadoes.

Fortunately, Walfoort was safely west of the circulation. And as the layered stack of clouds drifted east like an airborne birthday cake, she witnessed a meteorological marvel.

Many other photographers captured the spectacle as well. See some of the other images and videos shared on social media are below.