I find it interesting and irritating that last year it rained and nobody whined about the weather or changing the dates....really, if you don't want to be out in the weather. Get a car. Oh, wait. People hide from the rain and cold when they have cars too....never mind.
I'm from WA where I grew up with less than mild temps and more rain than I could fill an ocean with. Rain is water. It gets you wet, it dries. MoGang and Ricky are going to keep the date on the same week because of what goes on in May...tourists, graduations, proms, and everything else. If this is really the only grip you have, learn to adjust....there's also a company out there who sells gear to combat the cold. They are called Gerbings. They sell enough heated gear to cover you from neck to toe if you need that much.
The only difference between riding when its clear and 70 and rainy and 50, or any combination of the 2 is what gear you put on. If you can't adjust, maybe mc ryding isn't for you.
Sorry if this offends anyone...wait...naw. I'm not. Its what needs to happen.