Rain was forecast but it cleared up — I was lucky.
Usage
ラッキー is a casual, cheerful exclamation for small strokes of good luck. It is lighter and more informal than 幸運 (good fortune) or 運がいい (to be lucky). It is frequently used as a standalone exclamation: ラッキー!
The opposite is アンラッキー, though this is less commonly used.