Atmospheric effects and precursors of rainfall over the Swiss Plateau

In recent years, there has been growing interest in characterizing atmospheric conditions prior to rain events using integrated water vapor (IWV) derived from ground-based microwave radiometers (MWR). However, the occurrence of rainfall depends on a myriad of atmospheric parameters. This paper uses a composite analysis method to analyze various atmospheric parameters that affect rainfall over the Swiss Plateau during the period 2011-2020. 1199 rainfall events generated from the TROpospheric WAter RAdiometer (TROWARA) with a 7 s temporal resolution are combined with fields from weather station records. Different weather time evolution characteristics such as IWV, integrated liquid water (ILW), cloud-bottom infrared temperature (IRT) along with meteorological parameters, temperature, pressure, relative humidity, wind speed, and air density are identified before, during, and after rainfall. Regardless of seasonality or rainfall duration, a sharp increase in the IWV, ILW, and IRT before rain, and all the meteorological parameters reach the extreme 0.5 to 1 hour before rain starts. IWV at the end of the rain is lower than at the beginning, and it filtered by the 10-min band pass filter fluctuates significantly before rain. Air density drops 2 to 6 hours before rain starts. The true detection rate for rainfall prediction from air density alone as one of the precursors reaches 60%. Applying all these parameters to jointly predict rainfall is possible to obtain higher prediction accuracy.