isallobar

1. (meteorology) A line joining points of equal pressure change during a specific time interval, especially over three hours.Examples: "Seasonal variations of atmospheric pressure are illustrated by the isallobaric chart […] which gives the differences between mean pressure in July–August, and in January–February. The position of the isallobars on this chart is largely indicative of the role of monsoonal factors […]"; "Successive values of pressure provide figures for the barometric tendency, permitting the plotting of isallobars […] This is called tendency analysis."; "If your barometer has dropped 0.05 of an inch in the last three hours, you are on the -0.05 isallobar."