I live in Michigan, and I learned many years ago that forecasts are vague. Unless they're calling for 100% chance of torrential rain, it's just a guess. My first year commuting I'd drive if they said there was a chance for rain, but that meant I rode like one day a week, because in Michigan there's ALWAYS a chance of rain. So I gave up and just rode. Most days it was clear anyway, and when it rained, I got to like riding in the rain.