Omon A. Obarein

1 Introduction Precipitation variability and trends are important to climate scientists because of the high-impact nature of precipitation and its potential to change in unpredictable and unpleasant ways with climate change (Dai 2006; Trenberth 2011; Trenberth 2014). The most consistent premise for global precipitation change is that global warming will intensify the global hydrological cycle and increase precipitation (Allan et al.

Keywords: Ensembles; Forecast verification/skill; Forecasting techniques; Numerical weather prediction/forecasting; Short-range prediction 1. Introduction Many industries and sectors of society use guidance provided by subseasonal-to-seasonal (S2S) weather forecasts, which cover the period between 2 weeks and several months (He et al. 2021), to inform decisions.

Abstract Accurate sub-seasonal to seasonal (S2S) weather forecasts are crucial to making important decisions in many sectors. However, significant gaps exist between the needs of society and what forecasters can produce, especially at weekly and longer lead times. We hypothesize that by clustering atmospheric states into a number of predefined categories, the noise can be reduced, and consequently, medium-range forecasts can be improved.