allobar

Any form of an element having a different isotopic composition to that of the natural element, and thus a different atomic weight.

An area where the atmospheric pressure changes.

Highlighted in Alfred Henry's 1916 manual, Weather Forecasting in the United States, pressure-change charts have their own terminology, with allobar describing an area where the barometric pressure has changed by 0.1 inch or more in 12 hours[…]