Hello, I don't have much to offer, I've actually tried to find out similar information myself without much luck. I do know that in Southern Germany at least (Munich area for sure), it snowed on May 1st and was off and on thru May 3rd at the very least. The attached is a photo taken by my Dad on the morning of May 1, 1945 in Munich, it was pretty snowy that morning.
I'd kind of like to know what he found out too, but then I noticed that he first posted his request in 2010. My suggestion was to research some old Farmer's Almanacs.German spies grabbed copies of these things because of their accuracy in predicting the weather. His last post was about a year and a half ago, so we'll probably never hear about what he did or did not find.