Rilke observed that it is in early Spring and early Autumn that the natural world changes most quickly, although doubtless this is the observation of a European. I seem to notice year after year that there is an early nip in the air from late August on. Here is a short poem on the subject, which takes its inspiration from the simplicity of imagist poetry.
Summer died between two pages caught in print. Turning to look all I saw was sun through mist over damp fields A gust of wind banged the kitchen door.