Clabber up

the weather's clabbering up to rain; the clouds are clabbering up

"You mean a storm's clabbering up."

"[It's] clabbering up to rain, looks like," he muttered,[…]

... clouds began clabbering up on the south-western horizon, and the sky became more and more lowery. It seemed likely that something dramatic might happen, so late in the afternoon I put on my bathing suit, told Beth to close the[…]