If you’re someone who likes to sit out front in a rocking chair as you stroke your chin wistfully and mutter “storm’s a-brewin,” have we got good news for you. A new weather system has been detected kicking off above the Indian Ocean, a kind of storm that's a bit like a massive puddle in the sky. Meteorologists call it an “atmospheric lake”.

The novel weather system was discovered by Brian Mapes and Wei-Ming Tsai as they were investigating atmospheric water vapor looming over the Indian Ocean, presenting their findings at the AGU Fall Meeting.

An atmospheric lake is a massive aggregation of water vapor in the atmosphere, which is slow-moving and can endure for days. Using satellite data that spanned half a decade, the researchers found 17 instances of atmospheric lakes that had held true for over six days. Their emergence wasn’t season-specific and sometimes acted as a precursor to tropical cyclones, a much more dramatic weather system.

The lakes didn’t spring up out of nowhere, instead forming out of what’s known as “atmospheric rivers”. We’ve known about these weather systems for a long time and they pretty much do what it says on the tin: form fast-moving streams or “rivers” of water vapor in the atmosphere. These rivers can pinch off and slow, forming a “lake” that can hold and eventually rain an awful lot of water.

Atmospheric lakes typically form from atmospheric rivers running in from the Indo-Pacific region. These fast-running rivers can slow as they cross to Africa’s east coast, sometimes forming into atmospheric lakes that can linger for days and bring a lot of rain. Considering the climate in this part of the world, it’s likely our shiny, new (to science) weather system plays a pivotal role in the environment.

“It’s a place that’s dry on average, so when these [atmospheric lakes] happen, they’re surely very consequential,” said Mapes to New Atlas. “I look forward to learning more local knowledge about them, in this area with a venerable and fascinating nautical history where observant sailors coined the word monsoon for wind patterns, and surely noticed these occasional rainstorms, too.”

Speaking of cool weather systems, did you know that rainforests can make their own clouds? A 2021 study found that the net cooling effect of trees is likely far more significant than previously thought as until now nobody had considered how their cloud-formation impacts the climate. Clever trees.

[H/T: New Atlas]