Point-to-Area Rescaling of Probabilistic Quantitative Precipitation Forecasts

Abstract

A probabilistic quantitative precipitation forecast (PQPF) is prepared judgmentally by a meteorologist based on a guidance PQPF. The predictand of a judgmental PQPF is the spatially averaged precipitation amount. The predictand of a guidance PQPF produced by a statistical model is the point precipitation amount. Therefore, a procedure is needed for point-to-area rescaling of the PQPF. Theoretically based equations for rescaling are presented. The equations incorporate two predictive parameters, which characterize the precipitation field being forecast: the quotient of the area covered by a precipitation cell to the area of averaging (cell/area quotient), and the degree of certainty about the precipitation pattern (pattern certainty factor). Both parameters can be judgmentally quantified by the meteorologist during PQPF preparation. The same parameters can be entered into an inverse procedure for area-to-point rescaling of the judgmental PQPF.