Airport doesn't join quickly on start-up.

For some reason (and I can't figure out exactly when it started), my Airport takes longer than it used to to "join" my wireless network when I start-up or restart. When I turn the machine on, the bars are grey, then after a few seconds, the name of my network scrolls next to the icon and it joins. I wouldn't mind this except for the fact that I use WeatherPop, and it is starting before the internet connection is available, so I get no data and have to manually refresh every time. I never used to have this problem. Any ideas?