When it snows, but there are no visible clouds above you!
I stood outside and feathery snowflakes fell, yet there was blue sky above me. I was told it is called "immaculate snow". Immaculate snow and rain are signs of Spring in the high-desert.
(See also "Immaculate Rain")
Scientific info available at NASA website, astrobiology.
Nobody in the grocery store parking lot seemed to care that the snow was falling from what appeared to be blue sky; likely because "Immaculate Snow" is is a usual sign of Spring in the high-desert.