...go to the accuweather website and click the link to unsubscribe from the feed. you may also find this link in the original email they sent to verify the account when you first set it up.
If you are referring to the BB push weather, then go to the push weather website on your BB (BlackBerry HELP!), and click "Delete" next to the AccuWeather entry.
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"the trick to forgetting the big picture is to look at everything close-up" -chuck palahniuk