Prediction of extreme events in precipitation and temperature over CONUS during boreal summer in the UFS coupled model

The predictions of extreme events by the Unified Forecast System (UFS) Coupled Model Prototype 5 of the National Centers for Environmental Prediction over the contiguous United States during boreal summer are assessed. The extreme events in precipitation and daily maximum and minimum surface air temperature in weeks 1–4 predictions are analyzed in the deterministic retrospective forecasts of UFS during 2011–2017. The spatial structures of the extreme events in precipitation are reasonably well predicted but with higher values. Although the predictions of the temperature are closer to observation over central and eastern parts of the US, the model fails to generate the extreme events over large western regions. There is no appreciable growth of forecast errors of extreme events during weeks 1–4. While the spatial correlation of the number of extreme events between the forecasts and observation is very low for precipitation and temperature, the correlation of the temperature per event is very high. The model is able to better predict the observed location and magnitude of temperature events whenever it can generate such events. The number of precipitation events in the forecasts is higher than in the observation but with less accuracy in location and magnitude. The influence of slowly varying modes related to El Niño-Southern Oscillation (ENSO), intraseasonal oscillation (ISO) and warming trend of the ocean on the extreme events are also studied. All three modes have enhancing influence on precipitation while only the ENSO mode enhances the maximum temperature events. The minimum temperature events are enhanced by ENSO and ISO but diminished by the warming trend.