Possible Clues:

• Line in one's alternative map, originally
• Mentioned under the weather? Could be a definite sign of hot spots!
• Temperature line more confused with this
• It's displayed by weatherman in his other map
• A hotline to the weatherman
• Curve of equal temperatures
• Mother is confused by line on a map
• Mother is over the line
• One's additional mark a feature of weather map
• Contour line of equal temperature