Udderly amazing

Walking home from Tottenham Hale tube station this afternoon, I spotted these incredible alien cloud shapes - here they are above Broad Lane. Giant blobs that looked like they were the outer layer of some vast canopy...back home, I turned to my trusty Cloudspotter's Guide (a wonderful book, if you haven't got it). And here they are: mamma clouds, named after the Latin for, yep, breasts. 'At their most dramatic, they look like a field of smooth, globular udders,' says Gavin Pretor-Pinney. They form under all sorts of clouds, but they're biggest and best under Cumulonimbus, storm clouds. Given today's stair-rod rain, that sounds about right.