1Weather is available as a free, ad supported application and a $1.99 "Pro" application, which does not have any ads.
If you'd like to remove the ads select "Get Rid of Ads" from the menu to upgrade to Pro. This is an in-app purchase and the ads will automatically be removed from the application.
(Please note that while the Free 1Weather app does not have any cost associated with the application, using either the free or Pro version of 1Weather is subject to your carrier’s standard data rates.)