ISABNORMAL LINES, in meteorology, lines upon a map connecting places having equal departures from the normal. A better term is isanomalous lines. Each parallel of latitude can be considered as having a certain normal temperature based on a general mean of temperatures at stations along that parallel. Places which are relatively warm for their latitude have a positive anomaly, while abnormally cold places have a negative anomaly.
As these anomalies are expressed in degrees it is easy to inter polate isanomalous lines, which can then be used to analyse the effects of ocean currents, continentality, etc. The method can also be applied to the mapping of abnormal weather compared with average climate for any selected small area.