To the Lighthouse -- "Whitening before rain"?

Question

From Virgina Woolf's To the Lighthouse: > It was fringed with joy. The wheelbarrow, the lawnmower, the sound of poplar trees, **leaves whitening before rain**, rooks cawing brooms knocking, dresses rustling - How do leaves "whiten before rain"? Is this something common to all plants? Additionally, is a "rook" a type of raven, or what is a rook?

Answer 1

Leaves whitening before a rain refers to the lighter undersides of the leaves flipping over in the wind so that they are in view just before a storm.

A rook is basically a European crow.