A November rainstorm is the whole subject here, but the poem's real interest is in how the speaker hears it. The opening is almost harsh: the sky "spews" rain, as if the weather were being sick. Yet the clouds are "silver ribbons," which is pretty. That mix of ugly and lovely sets up the odd tone of the poem.
Then comes the surprise. The steady patter on the roof, which never lets up, becomes Beethoven's fifth symphony played by a ukelele orchestra. The comparison is funny, because a grand, dramatic piece is being plucked out on tiny, cheerful instruments. It also fits the sound well: thin, many-fingered, repetitive tapping. The setting, a park on a moonless night, adds a sense of dark, damp, slightly absurd loneliness.
The speaker seems amused rather than upset. They sit indoors, listening, and turn a gloomy evening into a playful concert. The mood is cozy, wry, and quietly imaginative.