Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I've had this problem too with my iPhone and by buddy did as well with his touch.

Try force-quitting the app (with the weather app open, press and hold the home button.) That worked for me once or twice.
 
Same thing happened to me. I have a backup wifi icon to weather.com/iphone just in case.

Just checked. Mine is working now. Danged, it's cold outside!

4D
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.