Lang grew up in Sussex and Hertfordshire. She graduated with a BSc degree in mathematics in 1991 from the University of Exeter, before joining the Met Office in 1991 where she prepared forecasts for the press, and presented the weather on local radio.
She joined the BBC on 31 May 1995, becoming one of the better known faces of BBC Weather, in part due to her distinctive red hair. She appeared across all of the BBC's TV and Radio news outlets, including regular primetime forecasts on BBC One and appearances on BBC World and BBC News 24.
She married Christopher Clarke in September 1997 in Hatfield, Hertfordshire. She had a son in September 2002 and a daughter in January 2004. They live in south west London. They are now Godparents to Amy Southwell born June 2000
- "College of Engineering, Mathematics and Physical Sciences - University of Exeter". ex.ac.uk. Retrieved 2 January 2016.
- "Isobel Lang has baby boy". bbc.co.uk. Retrieved 2 January 2016.