ME (bias) for Forecast Scenarios

Compare the ME for the different forecast scenarios of the fast-response and slow-response groups. There is an increasing negative ME, or under-forecast bias, with increasing lead time. But notice how the two scenarios with QPF perform much better than the two without.

Mean Absolute Error (MAE) for Different Forecast Scenarios as a Function of Lead Time for Response Groups: Slow, Med, Fast

Question

Why do you think that the persistence forecast would have the best mean error values with increasing lead time? (Choose the best answer.)

The correct answer is d.

Mean error plots for slow response basins averaged together; studied by the OHRFC

The mean error is also the additive bias. It can have an ideal score of zero if there are equal amounts of errors in both the positive and negative direction. The MAE showed us that persistence has the largest absolute errors of the different forecast scenarios.

Mean absolute error plots for slow response basins averaged together; studied by the OHRFC