Four lines, one image: the March wind as a playful little dog. The speaker compares it to a Pomeranian, a small, fluffy, energetic breed, and then switches to a second picture, a red rubber ball bouncing along. Together they make the wind feel less like weather and more like something alive and mischievous, full of "rambunctiousness" that can't sit still.
What the wind does is the heart of it. It bounces away "the long cold dark," meaning the winter that has dragged on. The speaker seems delighted by this, even relieved. Winter is treated as something heavy that a bit of silliness can knock aside.
The mood is bright, light, and quick. The bouncing sounds in the words themselves, with their short, springy rhythms, and the red of the ball adds a spot of color against the grey of the season being left behind. It reads like the first real feeling of spring arriving.