On Friday, May 1, 2020 at 11:52:26 AM UTC-7, Dave Nadler wrote:
On Friday, May 1, 2020 at 2:15:18 PM UTC-4, john firth wrote:
This is often called "thermal wave"...

https://www.ssa.org/Contests?show=blog&id=4169

Thank you, Dave, for that write-up.

On the Canadian prairies, the clue to thermal wave is a shift in cloud orientation. Takes a bit of wind, so typically a day with well defined streets up and down the wind. Abruptly, over a period of only half an hour or so, the skyscape changes - perhaps all of it, perhaps only one large area - to bands of cloud across the wind. Time to go wave hunting! Pressing forward into wind at cloud base, as others have said.

Sometimes, rather dramatic lennies cap the cu, but not always, and not the first clue.

Cheers, Bruce