When we broadcast a signal, some of it disappears off into space and is lost. Very occasionally, under certain weather conditions, this signal can instead be received much further than it would normally be. If you receive this additional signal it can potentially cause picture break up. The impact is variable and can happen for a few minutes or possible for a small number of days. There is nothing than can be done the problem will go away when the weather changes. For more information see our effect of tropospheric ducting on Freeview help guide.