The GOES-R Algorithm Working Group (AWG) Hydrology Algorithm Team is developing a 0-3 hour Probability of Rainfall algorithm for application to GOES-R data. The algorithm utilizes GOES-R current rainfall rates, forecasts of instantaneous rainfall at 15-min intervals and 3-hr rainfall potential, from the GOES-R Rainfall Potential algorithm to retrieve the probability of accumulating at least 1.0 mm of precipitation during the next 3 hours. The algorithm is being developed using products retrieved from EUMETSAT Spinning Enhanced InfraRed Visible Imager (SEVIRI) data as a proxy for GOES-R Advanced Baseline Imager (ABI), and the initial evaluation has been preformed against Nimrod radar data from Western Europe. The algorithm description and validation results will be presented along with additional planned work.