The Mesoscale Model 5th Generation (MM5) is used for operational support to Air Force missions in the Alaskan Theater. The Polar MM5 (PMM5), developed by the Byrd Polar Research Center for the high latitude ice sheets of Antarctica and Greenland, is tested over the Alaskan domains used by the Air Force Weather Agency to help mitigate the excessively warm surface bias of the MM5 identified by forecasters at the 11th Operational Weather Squadron. The verification of surface temperature, pressure and wind as well as upper-air temperature, geopotential height, and relative humidity of 27-hour PMM5 forecasts are compared to the MM5 forecasts to assess the differences between the models’ accuracies. A paired t-test is used to provide a statistical relevance to the model differences. A grid-to-station inverse-weighted linear interpolation technique is used to compare model output to surface observation for 71 locations and to radiosonde upper-air observations for 7 locations. The root mean square error (RMSE) and bias results are based on 67 forecasts made over a 4-month period during the Fall-Winter of 2001.

The PMM5 exhibited an average surface temperature bias improvement over the MM5 for all forecasts. The average surface temperature RMSE values were statistically identical between the two models. The higher PMM5 RMSE than bias is a result of the model residual variance for several stations. The model differences of all other fields fell within the measurement accuracies. The lack of assimilated snow cover may be responsible for the warm bias of both models in the winter months. The analysis of horizontal features and comparison of domain biases suggests a more physically realistic solution of the PMM5.