In article ,
says...
What sort of weather phenomenon woudl cause clouds like this?

http://www.ksntv.com/news/coolwxpics/default.asp

And here..

http://forums.somethingawful.com/sho...readid=1568989


I've seen them most often when you get a large area of cold outflow on
the back side of a storm. There's still enough convergence to get
forced ascent, but not well organized. The layer above the cloud is
almost certainly stable in the post-convective environment so the
vertical extent is limited. In effect, you're seeing the top side of
turbulent flow.

Harold

--
Harold Brooks
Head, Mesoscale Applications Group
NOAA/National Severe Storms Laboratory