"Nonaquatic birds bathing themselves are a sign of rain or storm. And a toad washing itself and frogs croaking more than usual signal rain. Likewise the appearance of the lizard which they call "salamander"; and furthermore a green frog singing in a tree signals rain... Likewise, if a tame duck makes its way under the cornice of a house and flaps its wings, this signals rain... If a cooking vessel filled to the brim emits sparks all over it is a sign of rain. Centipedes in large numbers creeping towards the wall are a sign of rain."
Theophrastus of Eresus, On Weather Signs (c. 300 BC)
Just face it: it's going to rain. (Also, centipedes in large numbers creeping towards the wall are a sign that you should call an exterminator.)