What's the weather? Give us something to work with. Light humor, dark humor? Weather report humor is usually local as well. You'd make a joke about having to move an event inside, or perhaps say something glib about having sun for a local picnic. Why are you writing this, anyway. Don't most weathermen just make it up on the fly?
It's humor like what SNL does. Something like, if you planning on going somewhere warm like iraq make sure you bring an army vest because of the flying bullets....
Watch "Good Morning, Vietnam" Maybe that will give you some ideas as to where you can go with this. Robin Williams is the master of improv.
Weather Humor...? Get out of that while you can. Don't even dabble in it. If you have to grab SNL and Good Morning Vietnam humor for this project, shoot yourself in the h- NO. Shoot the weather man in the head. He deserves. Get's all that money but can't even tell the sunny days from the cloudy ones.