"Weatherlawyer" wrote in message
oups.com...

I would go for a dust devil (which might not be betrayed by dust of
course if it formed over a surface that had little or no loose
debris.)

Any record of frost before them?


.... no recollection of such. That's not to say that the overnight
temperatures wouldn't have been on the low side (say 8-12degC), given
the dry spell we were then in and the character of the soil in the area.

Martin.