Mother is producing a line on a weather map (8)
I believe the answer is:
isotherm
'a line on a weather map' is the definition.
(I've seen this in another clue)
'mother is producing' is the wordplay.
'producing' is an anagram indicator.
'mother'+'is'='motheris'
'motheris' with letters rearranged gives 'ISOTHERM'.
(Other definitions for isotherm that I've seen before include "Line joining places of equal temperature" , "meteorological line" , "Contour line of equal temperature" , "Weather map may show that" , "Line of equal heat" .)