Abstract Operational forecasters are highly dependent on the atmospheric models that are run several times a day at the National Centers for Environmental Prediction. These models have inherent biases that can be identified over a period of time and used to improve model forecasts.
Models also exhibit forecasts problems that can lead to serious errors.
These can be due to initialization, lack of data over oceans and Mexico, incorrect terrain modeling, non-linearity of the atmosphere and approximated model physics. Forecasters that can identify model biases and errors can sometimes significantly improve model forecasts. QPFs have become increasingly important in the daily forecast routine at every NWS Forecast Office and River Forecast Center in the United States. These forecasts are used as input for computer simulations of rivers across the United States with the results helping Hydrologists and Meteorologists issue Flood Watches and Warnings. Due to model biases and errors, QPFs produced by computer models are only somewhat correct.