An ontology representation of severe weather based on the W3C standard is proposed. According to the understanding of the concept definition, naming and categorization, the concepts of severe weather are logically represented with a step function expression and a first order logic expression. The logical representation is applied in the ontology design, in which the class tree, the class of equivalent axiom, and the collections of object properties and data properties are built up, as well as the ontology library. By the intelligent agent, the surface observation of weather data is transformed into knowledge of meteorological disasters. The ontology library of the severe weathers built with the proposed representation is tested in the near real time GIS mapping and Web posting system. The positive performance in the automatic warning analysis of severe weather proved the efficiency of the ontology representation.