Actually, WIWN. I presume it stands for "WIsconsin Weather Nation". I believe it went on the air from Milwaukee on Tuesday.
The antenna is on the MPTV tower with channels 10 and 36. (and if I recall properly, several other stations) In the general vicinity of Shorewood.
From a legal standpoint, it's technically a Fond du Lac station. It was first authorized in 1987 and was first licensed in 2000. (it may have operated under its construction permit before that) For quite awhile it was authorized to operate from the same site as Trinity Broadcasting Network's channel 52 in the general vicinity of Holy Hill. I'm not sure it actually ever operated from there. To the best of my knowledge, the last site it actually operated from was a small, low-power facility within the city of Fond du Lac.