I agree with the above poster.
It really depends on which way the wind is blowing at the time.
I live in Brandon, about 45 minutes away from Disney, and I can barely breathe outside if the wind is blowing in the wrong direction. However, I have severe asthma, and my lung function was already comprimised before this. In Hillsborough County, where I live, all schools and daycares have to hold all activities inside ... so it certainly is something to worry about.
I called Disney about this, since we are leaving to go for the weekend next week, (and I'm a huge worrywart) and was told I could cancel since with my asthma I shouldn't be allowed out in the air. I have been looking forward to this trip for month's now, so I'm praying for some rain.
I asked the CM about if their was a hotline to call for weather or if they updated anything on their website, and she asked and there isn't. However, they do recommend if you are worried about the air quality, that you can call and get an update on how it is at the parks at that time.
Also, depending on how you're getting to Disney ... some roadways have been closed if the fire is to close to the Interstate. If you're driving, this is something you might need to look into. I know the Florida Turnpike near Kissimee was closed earlier this week.
I don't want to frigthen you, but it's something to think about.
Enjoy your trip!