The poem, by William H. Davies:
My mind has thunderstorms,
That brood for heavy hours:
Until they rain me words,
My thoughts are drooping flowers
And sulking, silent birds.
Yet come, dark thunderstorms,
And brood your heavy hours;
For when you rain me words,
My thoughts are dancing flowers
And joyful singing birds.
I believe the author is describing the creative process of writing. The thunderstorm is a metaphor for the author's mind, or perhaps his muse. He also personifies the thunderstorms by saying that they "brood for heavy hours" - meaning he sometimes has to concentrate long and hard, and still comes up with nothing - "raining empty words." When this happens, and he is not inspired, his thoughts are drooping flowers - another metaphor for lifeless thoughts, nothing that can be written perhaps. This emptiness of creativity is also referred to as "sulking, silent birds" - the birds are silent because he has come up empty.
In the second stanza, the tone changes. He addresses the thunderstorm (an apostrophe) and asks for the "heavy hours" because in spite of the difficulty, it is the only way to come up with the "raining words" that he can fashion into writing. When this happens, and he can write what he is thinking, then his thoughts are "dancing flowers" and "joyful singing birds."
This is a short little poem, but it is rich in metaphors.
What do you think? Could you interpret the thunderstorm as something else? Sure! It could be the author is planning on speaking to his lover and cannot come up with the right words to say. But I like the writing metaphor.