isobront noun2 •An isoline drawn through geographical points at which a given phase of thunderstorm activity occurred simultaneously. •An isoline drawn through geographical points which, on average, experience the same number of thundery days per year.On these charts isobronts, or lines of equal frequency of thunder, were drawn. These are shown in Figs. 1, 2 and 3, the data being expressed as percentages of days on which thunder was heard. — 1925 formsisobronts
