When to trim back Weeping Cherry tree?
 

First, I am a guy with no green thumbs....
We have what I believe to be a "weeping cherry" in
our front yard near the house. It is getting big enough to
possibly run into the overhangs. I would like to trim it
back and have done so in the past, but it started to bloom
two days ago. If I trim it back, will I do great harm??
Thanks
Tim R.

emails to

Thanks