Weed killing if its going to rain

[Chippychop]

Is it worth spraying weed killer if its forecast to rain??!!

No. It will wash straight off.

I need to do the weeds in the the path in the garden and and waiting for a hot dry (not too windy day) as it needs to stay on the leaves for a while to be absorbed.

Thanks I know it may have seemed an obvious question but I thought it best to check. I'll choose another job then...