What you see: On a given plot you will see a horizontal 0 line. Model Bias is plotted over the past 7 days for three models (ETA, NGM, and MRF). Bias is calculated (see next paragraph for more detailed explanation) for heights, temperatures, and relative humidity. Therefore, the closer the plotted lines are to 0...the less bias the output model field has (and vice versa). The plots are designed to give you a quick method of determining which model has been performing best over the past week (large scale pattern) for heights, temperatures, and relative humidity.

How its derived: The Bias (forecast - observed) is calculated for each upper air site over grid 212. The observed value is an upper air observation and the forecast value is the bi-linear interpolated model forecast (that is since the upper air sites don't correspond exactly to one grid point, a linear interpolation of the 4 closest grid points is used to compare to the observed data from the upper air site). The bias is then calculated for each upper air site and totaled to give an overall bias of a given model field for a given cycle. Although veiwing the bias over such a large domain does not allow you to acertain regional biases...these plots are designed to give you a quick method of estimating which model has been performing best over the past few days.