boofhead
The program you want to compliment FSX is Active Sky, it's a payware program that allows you to change the weather at any "weatehr station" i.e. airport. You can create a wx template then apply this as required.
This works great and is better than anything on the market so far
Click
here for more details but please be happy that it'll do what you want it to before buying it on my say so.
Here's a picture of the wx configurator, but please note this is ASV for FS2004, so the FSX version should be more advanced. You can set the distance from the weather station you wish the weather to go to as you can see.
CC