Sudden weather changes tend to occur with sunup and sunset due to rapid warming/cooling. This coincides with typical commutes.
I used to carry a lightweight rain parka that I used infrequently in Southern California, but often in the Wash DC area, especially springtime and summer afternoons.
One of my regular rural exercise ride routes heads directly east and west, with few wind breaks. On late afternoon rides it's pretty common for the wind to be in my face both directions, as it suddenly shifts directions around sunset.