Examining the Diurnal Cycle of Precipitation in the NCEP Global Forecast System

Forecasting the diurnal cycle of precipitation over the continental United States (CONUS) is a problematic process for most global forecast systems. A majority tends to have a strong bias and they don’t provide a skilled prediction of the intensity, coverage and frequency of the diurnal cycle. Accurately forecasting the diurnal precipitation cycle, is closely related to the overall quality of the global forecast itself. Also, the accuracy of representation of physical processes in the models is indicative to the forecast skill. Major implementations have been made for the National Center for Environmental Prediction (NCEP) operational Global Forecast System (GFS) throughout the years to make improvements to the diurnal cycle of precipitation. This study examines the diurnal cycle of precipitation over the CONUS during the winter and summer months of 2016-2017. The operational and experimental GFS will be analyzed and compared to the observed diurnal cycle of precipitation. To accomplish this, 3-hourly averaged accumulated precipitation vs. forecast hour plots, for the different models, were created. This allowed us to gain insight on how the skill of the models were performing, against the observations.

This study is expected to provide feedback to the model developers at NCEP’s Environmental Modeling Center (EMC) to inform (for making further) priorities for improvements to the GFS model, especially with the newly selected Next Generation Global Prediction System (NGGPS) Finite Volume Cube Sphere (FV³) modeling system. The NGGPS is a fully coupled system that will be designed to create useful forecast guidance out to 30 days, extend forecast skill beyond 8 to 10 days, and improve hurricane track/intensity forecast.