Dust in the wind.

Whoops! I started a phrase discussion a few days ago, and then that whole board went into archive. Here is my original post plus a single reply to date, from bob:

I am curious to learn whether people here have some good phrases or images for ephemerality. To give an example, one that I know is a simile: "fading like dew on the grass of a summer's morn".

to which Bob added:

Like a pork chop in a boarding house.

A snowball in hell

I'll look in a descriptive dictionary and see what I can find. All I can think of at the moment is the old song, "Dust in the Wind." That song is full of fleeting moment phrases.